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Hey guys, got a very interesting electrical issue that popped up and can't figure it out after diagnosing for a few hours. Here's what I know...
1985 IROC - Carbureted
Added after market electric radiator fan
Car didn't come with electric fan (I think) so I wired this to a relay that gets a 12v feed from the ignition when turned on.
Car sat for about 8 years, charged it up, and I noticed that the fan was not coming on with the ignition like it always has in the past. I've never had ANY issues with this setup and I haven't changed anything.
Multimeter came out, I see the signal wire only has .3v with ignition on and 0v with it off.
After a long diagnosis process, I realized that I have this fan signal wire connected to the choke heater relay.
Confirmed the relay is working properly on the bench.
I found that the ignition gives the relay's first pole 12v (from the C/H fuse), second pole is the choke heater device (now fan signal) at 0v, and third pole (from gauge cluster fuse?) is only getting the .3 volts.
The original wiring diagram shows the third pole that's getting the .3v coming from the gauge cluster. See highlighted attachment below.
I checked all the fuses and they all have 12v on them and all fully intact.
I really don't want to tear the entire harness apart trying to track this down... I don't even think I could with the small amount of space under the dash. Any one have any ideas at all where the heck this is fed from and why it would only have .3v with ignition on? Wiring diagram shows it is directly connected to the gauges fuse but like I said, checked all fuses and they all have a solid 12v.
Another thing I found while mind effing this is if I put the volt meter leads on a positive 12v pole and on the the third pole mentioned above, meter shows 12v. Could this mean its a short? Also, I did a continuity test between the third pole and all of the fuses and did not get ANY ringing from the multimeter indicating that the third pole is connected to any of the fuses. Super weird and I'm very very confused.
Also, side question... How the heck does the choke heater work? From the wiring diagram it looks like the choke it always on as long as the ignition and gauges are on. Something would need to disengage the choke one the car is warm, right? Maybe I'm reading it wrong... electricity is not my strong suit!
All help extremely appreciated!!!
Last edited by propaintball96; 12-30-2023 at 01:02 PM.
Just did a couple more checks and found the following...still no progress. Even more confused.
IGNITION OFF - RELAY OUT
1. Third prong female end has 0v
2. Second prong female end has 0v
3. First prong female end has 6v on it (Wtf?)
4. No continuity through the fuses and the third prong female end
5. C/H Fuse #4 & Heather/A/C Fuse #8 both have 6v on it with ignition off.
6. Getting -6v across the 2nd prong and the C/H Fuse #4. Same with the 3rd prong.
IGNITION ON - RELAY OUT
1. Getting continuity between the Choke Heater fuse and third prong female end
WTF?!
Last edited by propaintball96; 12-30-2023 at 03:26 PM.
I added the wiring diagram with some markups showing what voltages I'm getting where. A photo of the relay I really don't think would be of any value. Let me know if you mean a photo of something specific.
The choke is operated by a typical bi-metal spring; it coils or uncoils as the temp changes. When cold, it closes the choke blade. The heater is electric, and raises the bi-metal's temp, allowing the blade to open gradually. It is designed such that it will not be supplied with 12V unless the alt is charging; this keeps it from being heated up if the key is on but the engine is not running. There is a certain amount of variation in the factory's wiring from year to year etc. but the same principle is used on all.
I strongly suggest that you get that relay off of the choke heater circuit. Not the right signal for it at all. Rather, if you still have the computer wiring harness under the hood, wire it with one side of the relay connected to the pink/blk wire circuit, and the other connected to a temp switch that grounds when its set point is reached. The factory located this in the pass side head, in the same hole that's for the temp gauge sender in the driver's side head, therefore between the #6 & #8 spark plugs.
Last edited by sofakingdom; 12-31-2023 at 01:59 PM.
The choke is operated by a typical bi-metal spring; it coils or uncoils as the temp changes. When cold, it closes the choke blade. The heater is electric, and raises the bi-metal's temp, allowing the blade to open gradually. It is designed such that it will not be supplied with 12V unless the alt is charging; this keeps it from being heated up if the key is on but the engine is not running. There is a certain amount of variation in the factory's wiring from year to year etc. but the same principle is used on all.
I strongly suggest that you get that relay off of the choke heater circuit. Not the right signal for it at all. Rather, if you still have the computer wiring harness under the hood, wire it with one side of the relay connected to the pink/blk wire circuit, and the other connected to a temp switch that grounds when its set point is reached. The factory located this in the pass side head, in the same hole that's for the temp gauge sender in the driver's side head, therefore between the #6 & #8 spark plugs.
Thank you for the reply! Your explanation along with the threads you shared were extremely informative. I definitely agree with getting this relay off of the choke heater circuit but any ideas why the choke heater relay is not operating correctly? It seems to me that it has to be a short on the side showing .3v.
Also, the fan relay I am running is a standard 4 prong relay that is set up to run if the ignition is on which I've never had issues with in the past. I have a complete aftermarket engine setup that doesn't currently have a temperature switch that I could use for grounding the relay. That being said, might be a good time to add one in cause this seems like a much more appropriate setup. The pink/black circuit is always on with ignition on, correct? So the relay wiring would be:
Wow! This entire situation was unnecessarily made to be very over complicated.
We are talking about a very basic, very small Electrical Circuit with nothing but One Single Pole Single Throw Relay.
I would make the Connections that you Posted, but with one slight change:
1 - Temp Switch (Ground)
2 - Black/Pink 12v Ignition Feed
3 - 12v Battery
4 - Fan
For the very first attempt to Turn-On/ Power the Fan...
Instead of connecting your Coil-Ground Connection through the Thermostatic ("Temp") Switch, Connect that Wire directly to a very Good/ Clean Ground-Location.
As long as you succeed in Turing-On the Fan, you can proceed to go back and...
Making the Coil-Ground Connection through the Thermostatic Switch.
Most of the Original Thermostatic Switches did not close until a Temperature over 220*F.
Some of the Secondary Cooling Fan Thermostatic Switches did not close until almost 240*F.
Absolutely horrible for the Engine Cooling System longevity (and the Engine itself OVERALL).
Wow! This entire situation was unnecessarily made to be very over complicated.
We are talking about a very basic, very small Electrical Circuit with nothing but One Single Pole Single Throw Relay.
I would make the Connections that you Posted, but with one slight change:
1 - Temp Switch (Ground)
2 - Black/Pink 12v Ignition Feed
3 - 12v Battery
4 - Fan
For the very first attempt to Turn-On/ Power the Fan...
Instead of connecting your Coil-Ground Connection through the Thermostatic ("Temp") Switch, Connect that Wire directly to a very Good/ Clean Ground-Location.
As long as you succeed in Turing-On the Fan, you can proceed to go back and...
Making the Coil-Ground Connection through the Thermostatic Switch.
Most of the Original Thermostatic Switches did not close until a Temperature over 220*F.
Some of the Secondary Cooling Fan Thermostatic Switches did not close until almost 240*F.
Absolutely horrible for the Engine Cooling System longevity (and the Engine itself OVERALL).
Is the slight change you're recommending the testing prior to using the coil ground switch? Also, great point with 220* set point. Any recommendation of a lower set point switch out there that exists? 200 would probably be the right number I would think.
You mention ".3V" here and there, but don't say what you're measuring against. That is, your meter has 2 leads, a red and a black; I'm assuming you're probing with the red lead, which therefore is finding ".3V" at these places; but you don't say where the black lead is connected.
Even with all that, if the relay coil has 12V on one side and ".3V" on the other, it should be operated. If the side of the coil with ".3V" - which also goes to the "Volts" light in that schematic - goes to the alternator, then you have one of the schematics that has the error in the relay contacts: the contact should be a normally closed rather than normally open. This makes it so that when the alt is operating it puts 12V on that brown wire; then, since both sides of the relay coil are at the same voltage, the relay drops out; and that then supplies power to the choke heater. The point you have labelled "Fan Signal .3V" is actually a hard mechanical ground; physically, it's the "bowl" looking part on the carb that contains the choke thermostat and heater. The voltage there never changes. With the alt NOT charging, the brown wire that goes off the page in your piece of the schematic, has ground on it via the alt internals, which should operate the relay, which should CUT OFF power to the choke heater, NOT supply power to the choke heater as that schematic indicates. IOW, all that stuff you typed up there about ".3V", seems to all be working mostly correctly. There is no "issue" with any of it that I can see in your description, except that your add-on fan relay needs to be disconnected from the choke heater circuit and hooked up as both VI and I described.
For the temp switch, there's a factory one you could get that operated at a lower temp, for Buick GN or some such, and you can get that one at a parts store. You can get any number of them from various aftermarket sources as well. Those include ones that go in the head, ones you could stick through the radiator to make the fan respond to the hot side water temp without probing the cooling system internally, and so on. Personally I don't think there's anything wrong with the 220° switch temp but that's just me.
Last edited by sofakingdom; 01-02-2024 at 08:44 AM.
You mention ".3V" here and there, but don't say what you're measuring against. That is, your meter has 2 leads, a red and a black; I'm assuming you're probing with the red lead, which therefore is finding ".3V" at these places; but you don't say where the black lead is connected.
Even with all that, if the relay coil has 12V on one side and ".3V" on the other, it should be operated. If the side of the coil with ".3V" - which also goes to the "Volts" light in that schematic - goes to the alternator, then you have one of the schematics that has the error in the relay contacts: the contact should be a normally closed rather than normally open. This makes it so that when the alt is operating it puts 12V on that brown wire; then, since both sides of the relay coil are at the same voltage, the relay drops out; and that then supplies power to the choke heater. The point you have labelled "Fan Signal .3V" is actually a hard mechanical ground; physically, it's the "bowl" looking part on the carb that contains the choke thermostat and heater. The voltage there never changes. With the alt NOT charging, the brown wire that goes off the page in your piece of the schematic, has ground on it via the alt internals, which should operate the relay, which should CUT OFF power to the choke heater, NOT supply power to the choke heater as that schematic indicates. IOW, all that stuff you typed up there about ".3V", seems to all be working mostly correctly. There is no "issue" with any of it that I can see in your description, except that your add-on fan relay needs to be disconnected from the choke heater circuit and hooked up as both VI and I described.
For the temp switch, there's a factory one you could get that operated at a lower temp, for Buick GN or some such, and you can get that one at a parts store. You can get any number of them from various aftermarket sources as well. Those include ones that go in the head, ones you could stick through the radiator to make the fan respond to the hot side water temp without probing the cooling system internally, and so on. Personally I don't think there's anything wrong with the 220° switch temp but that's just me.
I was measuring with the red lead on the brown wire that goes to the volt light and the black lead on a body ground. I didn't believe the relay was operated correctly since I put a separate 12v feed on the brown wire (that was showing the .3v feed) and the relay snapped and the fan came on. After reading through you message though, this does make sense. It's just very very odd that this set up as it currently sits was working previously and just stopped...
I just ran into the garage and confirmed that I do not have the alternator hooked up to a brown wire. I only have the alternator connected directly to the battery and then connected to a slightly larger gauge red wire in the harness which goes back to the wiring harness C100 block and I believe is the power distribution to the fuse block. I deleted quite of bit when I dropped the new engine in about 8-9 years ago.
Bear with me here guys... I just peaked at my existing coolant temp sender (single prong). I have it hooked up in the passenger side cylinder head to green cable which gets lost in the wiring harness. Will need to do some investigation to find out where exactly it goes... That being said, does anyone have a wiring diagram for a 1985 radiator fan relay everything I'm finding on austinthirdgen and other thirdgen.org posts don't show a fan relay. It does show a temperature sensor connected to the ECU but its a two prong and goes to yellow wire. Maybe this explains in my other post why the gauge may be reading inaccurately? I swore I replaced this with exactly what it had prior to the engine swap which was a single prong temp sending unit.
Last edited by propaintball96; 01-02-2024 at 09:37 AM.
Factory fan relay, if your car has it, should be on the firewall near the brake booster.
Temp switch wire should be dk grn w wht stripe.
To identify the relay, look for one with 4 wires: pink/blk (I think), dk grn/wht, and 2 large thick wires, I think an org and a blk/red.
Interesting that the ECM and gauge are unrelated. Gauge sending unit is in the driver's side head between #1 & #3 plugs. Single green wire.
I have two relays in that corner. One is the throttle kicker I believe (5 wires - green, dark green, orange, brown, black) and the other is a 4 pin that has tan/white, orange, brown/white (which looks red/white in the attached photo), and orange. Can't find anything in the wiring diagrams that matches this.
Last edited by propaintball96; 01-02-2024 at 11:09 AM.
That's not a fan relay. There are no wires that are large enough. Its wiring looks REAL rough though, likely to be causing problems of its own with whatever it is. Same for that other thing below it with the red tape on the one wire and the butt splice on the other. Painful to imagine what the rest of it might be like. If Skillet has got loose in your car with his dykes, and the car looks like that in other places as well, it's no wonder you're having bizarre electrical problems.
If your car didn't come with electric fan, it won't have the relay for it.
If the wire you found by the pass side head is green w/ no white stripe, and there's not a green wire w/ no white stripe on the sending unit between the #1 & #3 plugs, then somebody (probably Skillet) has moved the gauge sending unit and re-routed the wire without updating your factory schematic.
That's not a fan relay. There are no wires that are large enough. Its wiring looks REAL rough though, likely to be causing problems of its own with whatever it is. Same for that other thing below it with the red tape on the one wire and the butt splice on the other. Painful to imagine what the rest of it might be like. If Skillet has got loose in your car with his dykes, and the car looks like that in other places as well, it's no wonder you're having bizarre electrical problems.
If your car didn't come with electric fan, it won't have the relay for it.
If the wire you found by the pass side head is green w/ no white stripe, and there's not a green wire w/ no white stripe on the sending unit between the #1 & #3 plugs, then somebody (probably Skillet) has moved the gauge sending unit and re-routed the wire without updating your factory schematic.
Any idea what that relay might be? I was trying to figure it out but nothing lined up to the wiring diagrams I found. I'd love to delete it if possible...Thats what Skillet would do, right?
By the way, whos Skillet? hahahaha thinking it might be me in this case.
I'm going to search around for the these wires and try to get back to an original setup. Appreciate your help!
No, I have no idea. If the wire colors aren't on your factory schematic, I can't begin to guess. I wouldn't just "delete" it though, until I'd figured out what it is.
Skillet is that guy that is proud of how poorly he did in grade school math & science, and now just want to "yank out all that computer junk and slap a carb on it", and THE FIRST THING he does when he thinks he has an electrical problem and sees some wires, is to cut a bunch of them, usually not leaving enough at the end to repair. He thinks all electrical problems can be solved by cutting and splicing. He talks alot about "grounds" but doesn't even understand what "ground" really is. He likes to add extra switches, a "kill switch" especially, but has no idea what they do or how they're rated or what kind of one to use for what application. He calls any and every electrical fault a "short". You've probably met him at some point in your life.
That other thing below it with the 2 big wires and however many others, looks kinda aftermarket. Might be worthwhile to figure out what that is too.
No, I have no idea. If the wire colors aren't on your factory schematic, I can't begin to guess. I wouldn't just "delete" it though, until I'd figured out what it is.
Skillet is that guy that is proud of how poorly he did in grade school math & science, and now just want to "yank out all that computer junk and slap a carb on it", and THE FIRST THING he does when he thinks he has an electrical problem and sees some wires, is to cut a bunch of them, usually not leaving enough at the end to repair. He thinks all electrical problems can be solved by cutting and splicing. He talks alot about "grounds" but doesn't even understand what "ground" really is. He likes to add extra switches, a "kill switch" especially, but has no idea what they do or how they're rated or what kind of one to use for what application. He calls any and every electrical fault a "short". You've probably met him at some point in your life.
That other thing below it with the 2 big wires and however many others, looks kinda aftermarket. Might be worthwhile to figure out what that is too.
I think I might know Skillet more than I'd like to admit... haha but then again...everyone probably has a little skillet in them.
The thing below the relay in the photo I sent is the C100 block to the right of the booster going through the firewall. Red is likely the power distribution to the fuse box and the pink/purple goes to the starter which I believe is from the clutch switch or ignition? Yellow connector came from the previous owner and if I recall correctly I wasn't able to get the pin out of the block so I left it and forgot about it behind the pretty wire loom.
Alright so I checked a 1987 wiring diagram with a coolant fan so I can wire mine up in a similar manner and I now have a theoretical question you guys....
Why do you need a 4 prong relay IF you have your 12v feed, ground from the temp sensor switch (signal), and your fan? The additional 12v feed from the fan fuse doesn't seem necessary if you just ran a 3 prong relay. Also, why would the fused 12v feed also need to be connected to the alternator as shown in the attached diagram? Seems redundant?
Last question, what's with all the fusible links shown throughout the wiring diagram? I feel like I haven't seen on of these throughout the entire vehicle?
Last edited by propaintball96; 01-02-2024 at 10:19 PM.
You need 4 terminals: 2 for the coil, which are a very low power circuit; and 2 for the contacts, which are a VERY high power circuit. Furthermore, the coil needs to have power available ONLY when the ignition is on, but the contacts need to get their power from as close to the battery as possible. You DO NOT want to force all that fan motor current to run through the ign sw to get to the relay. Even if there WAS a big enough wire in the ign circuit for the wire not to burn up that you could tap into somewhere, the VERY HIGH fan motor current would burn up the ign sw. Altogether the wrong way to feed it. Needs to be fed hard batt on the contacts, but ignition (at low power) on the coil side.
That particular wiring diagram covers a fan that is driven ONLY by the ECM. Doesn't show a fan switch at all. The ECM pin D2 grounds the coil of the relay to operate it; you'd simply wire a fan switch to do the same thing. Note that the wire color from the ECM to the relay is dk grn w wht stripe, as described above for the fan switch. Funny how the General is consistent with wire colors most of the time.
The brn wire from the alt allow the fan to come on only if the engine is running. Not quite the same discipline as using the pink/blk circuit, but the pink/blk is safer to hack into.
The fusible links are there to keep your car from burning to the ground in case one of the Big Red Wires shorts to ground. If your car doesn't have the same Big Red Wires, such as if it didn't come with an electric fan, then it won't have that particular one, since there's no Big Red Wire feeding batt to the fan relay for one to protect.
WOW! That was revolutionary for me. Thank you for explaining that. I now totally understand why these relay's are very specific the way they need to be hooked up to each pole.
I still don't understand the brown wire from the generator though. Its also hooked up to "Run" on the ignition according to the diagram so if the ignition is on and the car isn't running, the fan would still fire up, correct?
Now, before I hook up my 12v ignition feed either to the brown or pink/black feeds... I found a "FAN" 10amp fuse in the fuse box. I followed the wires and it has a red wire going to the ignition and a black/brown wire that disappears into the harness and looks like it heads to toward the passenger side of the car. The fuse is in position #2 in the fuse block which states "10amp Fuel Pump, Engine Cooling Fan, Choke Heater". Is this possibly a more appropriate circuit to run the 12v signal to the fan relay off of?
Right now I'm wiring the relay as shown below:
30 - Direct to Battery (High Power)
85 - Temp Switch - Ground
86 - 12v Switch to Ignition (Either to brown, pink/black, or the FAN circuit I mentioned above?)
87 - Fan
The brown wire is grounded by the alt internally when the alt isn't producing power. That's what turns on the dash light. It goes to 12V, by way of the alt's output, when the alt is working. At that time it can, in a perfect world, supply 12V to the relay coil.
Since your car didn't come with that feature, it's much safer to use the pink/blk circuit for the 12V side of the coil; a WHOLEHELLUVALOT easier to avoid catastrophic random results and future VERY hard-to-pin-down malfunctions involving things like ... charging the batt.
I'd use the pink/blk one if it was me, and err (if there is in fact any error) on the side of caution.
The brown wire is grounded by the alt internally when the alt isn't producing power. That's what turns on the dash light. It goes to 12V, by way of the alt's output, when the alt is working. At that time it can, in a perfect world, supply 12V to the relay coil.
Since your car didn't come with that feature, it's much safer to use the pink/blk circuit for the 12V side of the coil; a WHOLEHELLUVALOT easier to avoid catastrophic random results and future VERY hard-to-pin-down malfunctions involving things like ... charging the batt.
I'd use the pink/blk one if it was me, and err (if there is in fact any error) on the side of caution.
Gotcha, that makes sense on the alts grounding to turn on the VOLT light but that isn't shown on the diagram I sent a couple posts up but maybe it is on the gauges diagram for that year...How the heck do you know this stuff?!
Fundamental wiring question for you... When scabbing into another circuit, like the pink/blk, what is the best area to tie into? Should I find this wire in the engine bay somewhere and splice in? Or should I splice in at the fuse box and try to get through the firewall? The latter sounds like a pain in the ***.
Many years as an electrical / electronic engineer and car hobbyist.
When scabbing into another circuit, like the pink/blk, what is the best area to tie into?
Find one as near as possible to where you want to mount the relay, and follow it back into the harness. Eventually you'll come to a splice, where the factory tied a whole bunch of them together. You could also start at the C100 end (since that's probably close to where you'll want the relay anyway), there's probably a splice not far into the harness from there. Make your connection there by soldering your add-in wire to the existing splice. I'd suggest going to the junkyard and getting a length of the right colors of wires for each run you need to make; it's MUCH easier to service later on when their colors match the factory's, if they're not like all black or whatever.
Many years as an electrical / electronic engineer and car hobbyist.
Find one as near as possible to where you want to mount the relay, and follow it back into the harness. Eventually you'll come to a splice, where the factory tied a whole bunch of them together. You could also start at the C100 end (since that's probably close to where you'll want the relay anyway), there's probably a splice not far into the harness from there. Make your connection there by soldering your add-in wire to the existing splice. I'd suggest going to the junkyard and getting a length of the right colors of wires for each run you need to make; it's MUCH easier to service later on when their colors match the factory's, if they're not like all black or whatever.
Diving into this install this weekend. Grounding question for you. Currently I have the fan ground lead directly connected to the battery. Lots of extra wire and more thing on the battery which I hate. Wanted to cleaned this up a bit / make it more stock installation by either connecting directly to the body or to another 'terminal' location that is more appropriate. Any recommendations or maybe you know where the original ground location for this wire was?
Quick update, got everything wired up, temp hit 220 and the fan fired right up and is working great! Just wanted to say thanks again for all the help. Learned a lot along the way! Found the pink and black cable under the hood and tied into that circuit. You'd be very proud as a ordered all correct colored cable per the original wiring diagram. Felt great doing it right! Excited to dive into the wiring harness next time I pull the motor and get the harness back to OEM. Thanks again! I'll post a pic tomorrow as well.
Thought id share a couple photos. Kept the relay near the battery where it currently was until I pull the motor for repaint in a year or two. Tried to make it as clean as possible with loom, heat shrink, correct wire color & size, connectors, etc. Once the motor comes out ill relocate all relays to one singular location and rework all of the wiring harness back to it original state but in new loom and correct lengths for the new engine. Excited to clean up the connectors at the fire wall as well they look like ****.
12-30-2023, 11:53 AM
