Vader

Alternator problem - I know it's in need of attention. After all, it has almost 49K miles on it. Upon starting the engine, the voltage will slowly creep to over 17.5, and I of course get the MIL for a "51" (overvoltage). I haven't damaged anything - Yet.

Normally, I'd be thinking about a failed regulator, grounded test pin, or failed diode in the regulator feedback circuit (not the main rectifiers) If I unplug the field connection then start the engine, of course I get no generation. If I connect the field, then start the engine, it will go overvolt and continue to do so after I remove the field connector.

All that is normal for a failing diode or FUBARed regulator. It simply self-excites after it is generating, but here's where it gets a little strange. It hasn't failed to the point of doing this constantly. It will do this for a start cycle or two, then return to normal operation, regulating voltafe at a dead-on 14.2V.

It first happened a week or so ago, and I only drove it once briefly since then, when it was "normal". It started normally today, but of course once I got onto the parade grounds and restarted, it decided to overgenerate. I limped through the parade route on the battery only, and got it home. It hasn't done it since.

I know the alternator will be coming out for rebuild, but I can't recall having seen one fail like this, then "fix" itself. I'm suspecting a slip ring insulator carbon contamination problem, since silicon semiconductors are not self-healing as selenium rectifiers can be. Anyone ever had this kind of thing happen and found a cause? It's an '86 with the older style integral regulator alternator, BTW.

Stekman

I'm sure it's crossed your mind, but i will suggest anyway. Have you gone over the grounds? My neighbors Mark VII did something very similar. The amp light would come on and the volts would steadily climb to around 18 or so. After a bit, the light would go out and the volts would drop to a stable mid 14's again. Almost as if it mysteriously "fixed" itself. Turned out she had a bad ground for the regulator, or thats what i think it was.

I installed a new regulator and a remote ground that ran from the negative battery terminal to the regulator body ( the little terminal on the mounting screw). I really don't know if the ground was at fault or not. The car was like 14 years old, so I just put in a new regulator without doing too much troublshooting. The remote ground i replaced because I know grounds can act up on older cars. (I did do a shade tree test on the alternator. Disconnect field, no charge. Full field, voltage climbed fast. This proved the alternator was working correctly.)

Just something to think about, though i don't know the similarities between the Mark VII's and your charging system. I just know what i have seen (albeit a Mark VII, a NON f-bod, so i don't know how credible of a source that is.) Hope that helps Vader. Best of luck.

And don't worry, the weird stuff doesn't revolve *just* around you. This is the same neighbor that jogs in sweat pants and a winter coat....in the middle of July.

Vader

O.K. - That IS wierd, unless your neighbor lives in southern Australia. I'm guessing not.

Thanks for the support. I should know more today when I get off my butt and pull the alternator for review.

Vader

She was actually very clean coming apart. Not too surprising for a teenager with low mileage:

Trickster

Is that some smoking there near the front of that capacitor?

Vader

No. The cap checks good. The diode trio checks O.K. The main three-phase rectifier bridge is O.K. as well. The 50 ohm wirewound is at 43 (O.K.), and the brushes and slip rings themselves are like new.

I did find a lot of junk and contamination on both the brush holders and regulator connections (internal to the alternator) and will see if that solves it.

Vader

Well, POOPEY!

The cleaned/checked alternator still does the same thing. The case is well grounded, the 'A' terminal is getting full battery voltage, and the 'B' terminal is reading 10.3-10.4 ohms to the power circuits. Before you jump on that one, the '85 and '86 TPIs are supposed to use a 10 ohm resistance wire, not 100 ohms as in other cars. There is also no in-dash idiot light for the battery. I removed the I/P just to check if they had installed a dummy load resistor in its place, but no. The would explain the use of a 10 ohm, since it doesn't parallel a light bulb filament. There isn't even a hole punched in the circuit traces for the lamp holder.

Back to the regulator, I guess.

Vader

O.K. That was the strangest regulator problem I can remember. Usually, they go bad and stay that way. The fact that it would "revive" and start operating again is a bit beyond me. Oh, well.

Stekman

Then maybe it was the regulator that was bad in the Mark VII....

Vader

It was made in Dearborn? EVERYTHING might be bad...

Stekman

That's just cold, Vader.

Eats5.0's

iTrader: (1)

Vader, could it have been the diodes breaking down under a load? Just a thought.

RED92BIRD305

i have this problem with my brake lights and paring light being connectred together and i have gone through everything and it is checking out ok. the sockets would seem fine. how would i be able to test them. and also where would i be able to just nuy a new harness and start from scratch

RED92BIRD305

oh yea i forgto to mention that the lights still do the same even with all the lights out not a single light in the harness but when i unplug it. the front lights work normally and the third brake light since they are not on the same harness. so i am guessing it has to be a crossed wire (harness is all taken apart it cant be) or a problem with one of the sockets.

RED92BIRD305

sorry about that i meant to make a new thread