Mikey1968

Hey all-had a question on something that has me puzzled. I have been trying to fix all the gremlins in my 80 vette with much success. A few days ago, I noticed that when I turn the car off, the Red battery light goes on in the car. It stay lit and doesnt turn off (until the car is started again).
This never used to happen, and the battery has a full charge. That said, I try to run the car every few days, so if their is some sort of battery drain, I dont see it....
Any idea of what causes this? and How to shut it off?
I also want to confirm their is no drain.
let me know your thoughts

Mikey1968

A little more info that may help diagnose the issue. I just fixed my power door locks by installing a new passanger side switch and new wiring pigtail for the passenger lock. They work great now-but battery warning light still comes/stays on when I shut off the ignition.

Also, only one of my blinker indicaters work on the dash now.....??

Steve2147

In all probability the issues are not related. There is a component in the alternater called a diode trio, not to be confused with the diodes that are part of the rectifier circuit. A punctured diode in this diode trio will cause the light to stay on. BTW, if you have a light on there is a battery drain. The light bulb consumes current.

To confirm it's the diode trio simply unplug the harness at the alternater. If the light goes out your problem is internal to the alt, the diode trio. If it doesn't go out you have issues with the dash board circuitry.
But, one thing at a time.

Steve g

Mikey1968

How hard is it/how do I replace the diode trio?

Steve2147

How handy are you? I find it quite simple, but I've been at this for 40 years.

Mark the alternater halves for correct indexing when reassembling. Split the case, the windings will stay with the rear half. The three nuts that hold the coil ends to the rectifier also hold the diode trio to the rectifier. Remove those nuts and the one screw holding the other end of the diode trio to the brush assembly/regulater. Reverse procedure to reassemble. Of course I wold go through the rest of the alternater. test the rectfier to ensure you don't have a problem there as well. Check condition of brushes and brgs.

Steve g

Mikey1968

Well I pulled the plug on the altenator, and ideed the light went out. Plugged back in, and back on again.
Question-will the diode make the altenator fail to charge the battery during operation?
Went for a spin around the block, and power seemed fine. Battery meter even increased slightly during use.
If it doesnt do its job, wouldnt it be easier and not too expensive to just swap out with a new reman altenator??
thoughts?

Steve2147

Yes, the alternater will still charge with the diode trio out. The diode trio's function is to operate the light.

Sure, you can replace the alternater. I like to keep things original (who knows, someday matching numbers might be important on a 1980) and I have difficulty spending $60-100 (depending on brand/quality) when a $12 part and 15 extra minutes after the alt is off is all it needs.

Steve g

M Pete

Hey guys, I'm digging up this old thread because I had the exact same symptoms as Mikey. I pulled the alternator plug and the light indeed went out. The pics below are of my wire harness ends which attach tot he alternator. At first I thought that they were charred. But it appears to be fouled by oil.

A. What could cause this?

B. Would this cause my problem with symptoms listed above?

C. What is the best way to clean the harness?

lvmyvt76

replace the end connectioin, any parts store will have them, just splice the wire correctly when doing this, or you will have other problems.