The Stovebolt Site Forums The Shop Area The Electrical Bay Alternator issues

Hey everyone, I have a problem.

I switched over to 12 volts using the EZ-wire harness a while back. I have everything working the way I like but I notice that when I have my headlights on the amp meter in the dash reads on the negative side.

I have a 94 amp alternator (12SI) from an '84 camaro (new). Shouldn’t this be strong enough? Is there a possibility I have some wires crossed somewhere that might cause this?

I have a 10 watt resistor that I understand should be in the alternator circuit somewhere, but I don’t know where, would this cause the problem?

I have also noticed that the alternator gets very hot to the touch after it has been running for a while, could this indicate a problem?

I really need some help with this one guys, I can’t figure it out.

Hey, Gecko

You can't do any better than your Delco 12si 96 amp alternator ... that's not your problem.

Your headlights should not be causing a draw though -- something isn't right there -- double check all your wiring on your headlights; make sure you have a good clean and solid ground.

You might consider headlight relays ... see This

Another thing that comes to mind is *where* your gauge is reading your voltage (amps) from. Many people piggy back the third wire to the alternator to the back side of the alternator and that is NOT the way to properly read voltage. I ran that wire to a terminal block I installed on my firewall (under the hood) where I run power to everything (like my headlights) and THAT tells my gauge how much power I have, where it counts; an honest and true reading. See This

Thanks Horvath, I read your site about a dozen times comparing it to my set up and found there were a few things wrong. I managed to get it hooked up properly and when I did the amp gauge shot up to the positive side and everything got a lot brighter. Thanks so much for the help, and thanks for documenting your system so well and so clearly for the rest of us!

I'm GLAD my articles helped you out, bro'!

It sure makes you feel good when things are done right, doesn't it?

It sure does, I spent the better part of yesterday trimming wires and eliminating unused curcuits. Under the dash now looks clean and tidy, not like a rats nest.

The amp meter tells you current is flowing, which does not always mean something is wrong.

If your amp meter is showing negative when the lights are on it means your truck is wired so that current to the lights is going through the guage.

That may or may not be a problem.

If you are using the stock amp meter your alternator may be able to produce enough power to burn out the guage. But unless you are running some accessories that use lots of power you are probably okay.

What wiring diagram did you use to wire your truck?

How is the alternator wired? Is it wired as a '1-wire'?

If your headlights don't pull some current they are burned out or disconnected. What that means to the amp guage depends on how things are wired.

I didn’t use a wiring diagram; I just copied what was original as I went along. I have wired the alternator as a 3 wire; I didn't piggyback any wires etc. I added the idiot light to the circuit from the alternator and now when I start the truck it will show a huge discharge on the gauge until I rev the engine a little, then the idiot light turns off and I get a strong charge for a minute or two then it tapers of to no charge/discharge on the gauge. I'm pretty sure everything is working how it should now.