Roblen91GTA

So tonight on my 1991 gta when i turn the headlights on or parking lights the radio lights go completely out but the radio still works... its the original radio, any help greatly appreciated.

Wife'sCar

iTrader: (1)

I'd guess the light switch is acting funny, the radio lights dim I believe when parking lights are turned on. The dimmer might be cutting out completely. Try spinning the **** back and forth, might have built up corrosion in the switch, do it in whatever setting the lights cut out.

Roblen91GTA

Yeah i was thinking headlight switch because i replaced it with a cheap part store brand type a few years ago. ill try messing with the dimmer like you said but if that doesn't work i think im just going to grab an ac delco switch

Roblen91GTA

I ordered an ac delco headlight switch on a hunch but is there any other things it can be?

Roblen91GTA

Can someone please give me some help/ideas, the new headlight switch did not help and i tried my brothers monsoon radio out of his 1999 trans am and it did the same thing headlights go on and radio lcd and back lights go out...and the dash lights do not go out.

Wife'sCar

iTrader: (1)

Now you need to be checking for wires shorting out. Check continuity from one end to the other on anything involving lights.

Roblen91GTA

Thanks for the reply again, not getting much help on this subject lol. i might have found the problem after searching around....i could send you the link if you'd like but it sounds like the remote dimmer. I ohm tested the connector (only 3 wires) going to i believe the radio harness and it ohm'd at about 30.0 on 200 scale and then i tested the actual part and got no reading it was reading infinite, so i will be going to the part store tomorrow and dropping about $40 on this remote dimmer part

90 GTA Black

Can you post the link in this thread? I have a 91 GTA that the radio buzzes when the lights are turned on. May be something similar.

Roblen91GTA

http://www.cvpi.org/archives/p71inte.../wsdindex.html

yeah it could be. i'm going to hit the part store soon to grab this part

Roblen91GTA

Ok wtf the remote dimmer did not help my issue and that really annoys me but now i really have no clue what this problem could be

Catheran

Possibly a faulty ground for the light circuit, could be in the base of the light itself,

Roblen91GTA

I've heard about one of the fusible links near the starter blowing but would that only isolate the radio lights going out when the headlights are on? plus i don't even know where exactly the fusible links are i just know they are near the starter...really don't feel like jacking the car up to look at stupid fusible links

bigal55

iTrader: (1)

You can throw parts at it, trying to fix the problem, or search the net for an answer, but that will be costly and time consuming. You had the wiring apart at the dimmer, did you check to see if you have voltage on those wires when the headlights are on (no radio lights)? My guess would be that the dimmer is working because the dash lights work off the same dimmer. The wiper of the dimmer controls the voltage to the lights, both dash and radio. You need to look at the wires to the radio and see where the light circuit connects with the dash light circuit, this is probably where you are losing the voltage for your radio. GL!

Roblen91GTA

Very true, so would you rule out fusible links by the starter? its very strange its just the radio lights going out and nothing else, also the radio still plays music while the lights go out.

Roblen91GTA

Just did testing and have voltage at the brown/black n red wires from the dimmer...but like you said the dimmers are fine because the dash lights are fine

Roblen91GTA

Ok after testing the harness with a volt meter the brown wire from the harness that goes into the radio drops voltage when the headlights go on, does anyone know where it could have a problem? i see it goes to the remote dimmer that replacing did not work, and most of the wires i can see are fine and most of my under dash area is taken apart.

RedLeader289

iTrader: (2)

I have the exact same problem. Haven't figured it out yet either.

bigal55

iTrader: (1)

There is probably some type of junction where the radio lights and the dash lights all come together, or maybe a connector in-between the radio and the dimmer. You will need a thin wire probe, that can get into the connector where the wire enters (backside), for your meter. With everything connected and the headlights on, test for voltage at the dimmer (brown wire). Rotate the dimmer and verify that the voltage goes up and down. With the dimmer set for highest voltage, trace that brown wire back toward the radio and test any points that look like a junction or connector. The brown wire should vary voltage with the rotation of the dimmer control and should go to a full 12 volts and down to zero volts. You can make a probe using a thin stiff piece of wire wrapped around your meter probe. Tape it up leaving just 1/4 inch of bare wire extended to probe the connectors. You should be able to find the spot where you are losing voltage. Hope you find the problem and get it corrected. GL!


1991 Pontiac Firebird Car Audio Wiring Diagram
Car Radio Battery Constant 12v+ Wire: Orange
Car Radio Accessory Switched 12v+ Wire: Yellow
Car Radio Ground Wire: Black
Car Radio Illumination Wire: Gray
Car Stereo Dimmer Wire: Brown
Car Stereo Antenna Trigger Wire: Pink
Car Stereo Amp Trigger Wire: N/A
Car Stereo Amplifier Location: N/A
Car Audio Front Speakers Size: 4″ x 6″ Speakers
Car Audio Front Speakers Location: Dash
Left Front Speaker Positive Wire (+): Tan
Left Front Speaker Negative Wire (-): Gray
Right Front Speaker Positive Wire (+): Light Green
Right Front Speaker Negative Wire (-): Dark Green
Car Audio Rear Speakers Size: 6″ x 9″ Speakers
Car Audio Rear Speakers Location: Side Panels
Left Rear Speaker Positive Wire (+): Brown
Left Rear Speaker Negative Wire (-): Yellow
Right Rear Speaker Positive Wire (+): Dark Blue
Right Rear Speaker Negative Wire (-): Light Blue

bigal55

iTrader: (1)

After posting the wiring legend for your radio, I noticed there are two wires for radio illumination. The brown wire is the dimmer circuit and there is a gray wire for normal illumination (full on with headlights off). Try applying 12 volts directly to the brown wire going to the radio and see if your radio lights come on (could be a problem with the internal radio lighting circuit).

Roblen91GTA

Thanks for all the info and diagram. i also tested for continuity between the remote dimmer, witch is the only place i can run down the brown wire besides the rotating dimmer and from the radio harness and showed good continuity.

I don't think its internal radio because i tried a monsoon radio out of my brothers 1999 trans am and did the same thing. This is for sure a very strange problem

Roblen91GTA

Just did more testing and get full 12 volt at brown / gray wire at radio harness, when i turn on the headlights the brow wire dips voltage and when i play with the dimmer going up it increase's voltage and down lowers it but with the gray wire up on the dimmer decrease's voltage and down voltage goes up all in small increments....is that normal?

bigal55

iTrader: (1)

Don't know if that is normal. Don't know the scheme they use to dim the radio lights, could be a combination of the two wires, gray and brown. I couldn't find a good schematic of your radio circuit and can only guess at this point. If you have an electrical drawing of your radio circuit (dash wiring), post it and we will see if we can figure it out, but with no drawing we can only guess. If someone has a drawing, please post it as I see there is more than one person with this strange problem.

Roblen91GTA

Yeah very true. in the mean time i think i'm going to buy the shop manual for the car on ebay for like $60 to trace the wires better, but if someone knows any other things that can cause this before i buy that would be great

bigal55

iTrader: (1)

Any more info here? Did you get the manual and does it have the drawing you need?

Roblen91GTA

I should be getting the shop manual in the mail on like Tuesday this week so we shall see if it has any info i would need, but i was on my way home from a car show today and it was getting dark flipped on my head lights and of course after all this the lights and display work again! and i was messing with wires all last week and kept trying it in my garage and wasn't working but it worked fine the entire time coming home. I really don't know what to say about that but i'm happy...for now

bigal55

iTrader: (1)

Would have been nice to figure out the problem, but good it is working for you. Probably a loose connection somewhere, hope it doesn't return. Intermittent problems are always the hardest to troubleshoot. GL!

Roblen91GTA

Yeah i wish i knew the source of the problem, it was strange that every wire i tested had good voltage and good continuity, probably why i was so confused and had nowhere to start but yea i hope it doesn't return. when i get this shop manual in the mail i will try to figure out the source of the problem for others with the same problem