IROCmenace

iTrader: (1)

88 5.7 IROC wiring not butchered, sorry long

I had an alternator (alt 1) on the car since I got the car 3.5 years ago. Had an underdrive pulley on it. It quit charging a couple weeks ago. I had an extra (alt 2) and changed it out, regular pulley. It charged for most of the day and then while running it went out. Since then I have:

- Charged the battery with a Battery tender, car runs off the battery now
When I pul the negative off the bat it dies
- I have had both alternators tested, alt 1 tested fine; alt 2 tested ok but was slightly weak according to the parts store
- I put alt 1 back in the car with the regular pulley and took the car on battery power to the parts store and tested it, battery good, no alternator output
- I check the fusible links at the battery and crawled under the car and checked them at the starter, all intact
- I changed out the 3 wire plug as it was deteriorated with a new one; I have the red to red, brown to brown and black to factory tan and white
- I have checked the fuses, including fan and gauge
- I checked voltage with a DMM back probing at the battery, and the harness at the alt, before and after the splices for the new connector and off the bat post on the back of the alt; they all basically read the same as the bat volts, 11.5 to 12.5; car running; one of the two smaller plug wires bounces all over the place while the other reads the same as the bat volts
- I have swapped the black and brown wires out with no effect
- I have ran a direct 12V to the brown and black at seperate times and still no change in volts and no charging

Note: I use an autometer gauge, the factory volt gauge is not in the car, it has charged with it gone for a long time but my searches revealed that on cars with volt lights the bulb has to be intact to ensure the excite wire works correctly. I couldn't find anyhting on if this matters.

I am at a loss. I am lloking for new ideas. I hate to buy a new alternator if it is something dumb and since they theoretically tested ok. Any help is greatly appreciated.

IROCmenace

iTrader: (1)

bump

hdis2002

iTrader: (1)

I've got an 87 IROC so my wiring is a little different from yours. I had an issue with charging and it turned out to be the charger wire. Does your car have one wire that runs from the battery positive straight to the alternator? Mine looked ok but a voltmeter said otherwise. Changed it and the problem went away. Put a 10 gauge on it.

IROCmenace

iTrader: (1)

Thanks for the reply. I was just getting on here to say that, even though I had two alternators checked on the machine at Advance and they tested good, they were evidently not good. I bought a new one today and now the car is charging again. We will see if it is short lived or if that was the issue. I am about to finally swap the motor out for one with the correct L98 heads, cam and a good crank so I will be changing all the battery cables at that point.