Hey guys, I'm working on my 86 S4, and the alternator went out on it.

I bought a new alternator and battery, and installed both, and now the car won't start, was there something I potentially missed? any ideas?

Expanded explanation!

Cars voltage would drop off at idle, tested at autozone and they said the voltage regulator was bad, and the battery was as well.

-Got a new alternator that had the B post in the wrong direction which i moved to the correct vertical direction.
-The new alternator pulley is smaller than the original one. I am using the new pulley with the alternator just adjusted to the correct tension for this smaller pulley.
-The new alternator front case was threaded like a bolt would go in backwards, so I drilled out the threads so the factory bolt could go through it to the other side.

When the alternator was just replaced the car was hooked up to my 240sx with jumped cables, and even then it would drop voltage into the ether and be at 0 on the gauge, with no cranking.
With the new battery, it cranks but the gauge still drops to around 10, cranks fine, but does not start.

 

Double check all the grounds? If on jumper your voltage is off then I would think its something mechanical like a ground, as you should read their voltage at that point (Also verify using a multi-meter if you have one in case your gauge is bad). Also, to rule it out you can unhook the new alternator/batt and run off the jumper cars current, so at that point if you had good grounds/wires/starter you should start fine. If you can't maintain voltage while jumped and the new parts out of the loop I'd look at the grounds and + cabling stat.

 

I replaced the 80a main, even though it wasnt blown, just on the off chance something internal was off. I pulled the battery and tried to jump the car via just the batt cables -> jumper cables -> my running 240sx battery and it drops volts and wont start, so i'm going to assume you're right on the ground/power cable issue, just weird how it was working before and now it isnt. Although the power side connector is the original one and its VERY chewed up. I may replace that just due to the fact its chewed up, and then try again and see if that gets me somewhere, then if not, trace down the wires and check all the mounting points to make sure everything is clean and secured.