Battery light dim

[Danno]

I'm slowly trying to work through my electrical issues. I just don't know where to start, there are too many overlapping issues, methinks. I've cleaned all the grounding circles or whatever they are called.

The largest issue is with the charging system. When I turn the key to ON my brake light and oil light come on and the battery/charging light has the faintest little glow. Start the car and the very very faint glow is still there. Barely visible in any sort of daylight, and only when I take the bulb out of the dash!

This leads me to believe I have a leak somewhere in that exciter system. Brad, I'm looking at the 79-80 wiring diagram from your site and it just makes me more confused. I'm following a light blue/black wire off of this bulb and according to the diagram it just magically turns blue/pink?

I just don't know.

[spider2081]

My diagram shows the power side of the charge light goes to the unfused side of fuse 1. It connects with one of the pink wires from the ignition switch and is hot in both "start and run".
The first thing I would do to check your circuit is, remove the field wire from the back of the alternator and ground it. If the light then lights bright the problem is in the alternator.
There is a 7 pin connector behind the instrument cluster that has both of the charge light wires in it. C24 my diagram shows the wire to the alternator changes color at this connector. From the light to C24 the color is Black. From C24 to alternator the color is black Violet
The diagram I am looking at is for 80-81 so you might have different colors but the path should be the same.

[Danno]

I'm using the 79-80 because I have a carbureted spider, but the path is essentially the same. I did not try grounding out that connection from the back of the alternator, but did try (unsuccessfully) jumping all connectors by using A clean second wire to that fuse and one to the back of the alternator.

So, if grounding that wire makes my light bright, is that a SURE sign of a bad alternator?

[spider2081]

One thing I forgot to mention, There are three terminals on some alternators. The stud terminal is the output and connects to the starter solenoid. There can be 2 push on Spade terminals. The one marked D+ is the one that connects to the charge light. the one marked + is for a radio noise filter. If the light i connected to the filter terminal the alternator and charge lite will not work properly.
So be sure your charge lite is connected to the D+ terminal.

I believe (not sure) the charge lite gets its ground through the voltage regulator when the alternator is not turning. When the alternator turns fast enough the D+ terminal has the same voltage as the B+ (output) terminal that feeds the light. The light then has the same voltage on both sides of the bulb so it does not light.

So if it works the way I think it does a bad voltage regulator (attached to back of alternator) could be the problem as well as the entire alternator.
You could take the alternator off the car and have it tested before purchasing a rebuilt.

[Danno]

Unplugged exciter wire from alternator and grounded it. That lit up my bulb instantly. Means a new alternator?

[giuliot60]

My battery light is always glowing, and from what I've read everyone has that issue unless they go to a 95 amp alt. I don't know how true that is. Although your explanation does make sense 2081.

[Danno]

So, has anybody replaced a diode on these before? I might take mine apart and replace the brushes and the diode for the exciter wire, but where do I purchase said diode? Do NOT tell me to take it to my local alternator rebuild shop. Such a place does not exist in my location. I thought I had a lead, but alas, the old gentleman there said he only repairs electric motors (I thought most of those places did both, but what do I know?)