Finishing up final issues on my VS build and hit a wall on charging issue. Car has Porsche 1600 motor, 12V generator, alt etc.. The vehicle is charging properly but the light on dash is not behaving. There is nothing at all with the one wire attached. If I ground the light separately, the light works but gets brighter as rpm's go up, dim at idle, the opposite of what I expect. I searched past similar issues and tried everything but no help. Any ideas? Thanks in advance, Scott
Replies sorted oldest to newest
One side (wire) of the dash light goes to +12 Volts on a switched circuit - it should have power when the key is on. This may be part of the lamp base as some of them get 12 volts through the plastic bulb holder base.
The other side of the dash light (what you may think of as a "ground") goes to the "D+" (small) wire on top of the alternator. When wired up this way the circuit becomes a simple "comparator", comparing the D+ signal to the battery level and lights the light when the alternator output voltage is lower than the battery charging level.
So, one side to +12 volts, the other side to D+ on the alternator.
First things first, do you have a generator or an alternator?
12V generator
If you ground the light, getting brighter with higher RPMs is normal as the generator is (should be) putting out more voltage as RPMs increase.
You say it is charging correctly, what voltages are you seeing when off, at idle, and at higher rpm?
You say the light does nothing. It won't even come on with key on and engine off? As you've already verified the bulb is good, that would point to a wiring fault or possibly a faulty regulator. Check continuity in the wiring going from the regulator to the light and clean corroded connections.
