I just recently had a 350 swapped into into my '91 RS....And it dies. Ive purchased 2 new batteries and it drained them. I tested the alternator twice and it passed. I just changed the Voltage regulator today and put a third battery in. It ran for 15 minutes, I pulled off the positive cable, and the motor shut off. I traced the harness and there is ONE red cable that isn't connected. Could this be the problem? I need help!!!

 

Welcome aboard thirdgen.org.

If you pulled the battery cable and the engine quit, for sure your alternator is not getting voltage to the system.

Where is the red wire that isn't connected?

 

Its was supposed to be connected the starter down below. The cable is long enough, has the right bends and everything..so, I called a buddy and we connected it. Aaaaaannd it still does it. He brought over a book that stated that the alternator is only supposed re charge the battery. NOT power the entire car while the motor is on. It also said that the cable IS NOT to be pulled off. So if that holds true, it HAS to be the alternator. Right???

 

With the car running, you can disconnect the cable from the battery and the engine should continue to run on the alternator (unless that changed with the later 3rd gens).

Check for battery voltage on the large wire at the back of the alternator. If you don't have voltage there, then you've still got a wiring problem - that should have battery voltage whether the engine is running, not running, key on, key off, etc.

The other possibility is the field wire has a problem. That should energize the alternator when the key is on.

If all of those things check out, then you may have a bad alternator.

 

Thats the only other wire that goes to the alternator right? I've never messed around with wiring and I want to be sure....And is it possible for the alternator to be bad and still pass tests? I believe so. I belive it will hold an X amount of energy but not enough to keep the car rolling for an extended period of time..Thank you Five7kid. I will test the wires and get back to you. Thanks again!

 

i've had the same problem, i had an 83 305 into my 88 sport coupe, i had to add a wire to the voltage regulator to the back post on the alternator to get it to charge