My LS3 swap into a 1990 C4 is just about complete and I was able to drive it for the first time today.

Of course there has to be a problem. My alternator doesn't seem to be charging at all no matter what RPM I'm at. It's a brand new AC Delco that came with my GMPP accessory drive and it has three wires in the connector. Can someone give me some tips on how to diagnose it? Searching seems to pull up information on the one and two wire alternators. My voltage is around 10.5 to 11.

Can the generic parts stores test this type of alternator?

Thanks!

 

They can test it

Search for "Thee alternator" thread and itll get you going. Stock, the alts are controlled by the PCM, but wiring them as a carb car is a simple fail safe method for reliable alt control

 

Mine did that when I first hooked it up. Discovered I had swapped the sense and charge wires. Simple fix. Like said above a parts store should be able to test your alt.

 

Alternator tested good. I did the resistor mod and it works great.

Thanks everyone.

 

what did you use for a resistor? gonna have to wire mine soon

 

1/2 watt 470 ohm

 

thanks! i knew i needed a 470ohm but wasnt sure on the watts..

 

I had the same problem.
I have an LS3 brand new everything in a 57 chevy pickup. I played with it for 2 days and finally someone told me the alternator needed a ground.
I used a #8 wire from the alternator to the block at a threaded hole just above the header. I used yellow wire ends on both ends and crimped them. Now when I start the car the gauge shows 14.3. And before it showed about 12.5.
I tried a #12 wire with alligator clips to various places and they did not work.
The only this works is with the wire securely mounted to the block and the alternator, not the valve covers or anything else. TRY IT

 

Did you paint or powdercoat your alternator bracket, or paint the engine? Because the alternator should be grounded through the bracket, but I have seen the bracket be insulated by paint.

 

Yes, I had the alternator bracket powder coated

 

I too had this problem and it ended up being my alternator bracket was anodized black and providing a ground. Make sure that any powder coated or painted piece has a good ground or run a wire off the front bolt. That should fix the problem.