Alternator power issues

Okay so my charging system has not been working properly ever since I got this build done. It will only hold 10.5-11.5 volts at idle. So I checked everything with a multimeter and that’s all the alternator will put out. It’s also I brand new j2 fab custom unit. My car is twin turbo so it’s in the valley like the older year cars. So I had to splice in a new 3 wire plug for the alternator and I’m pretty sure that’s my problem. So does anyone have any idea what wires in the stock harness tie into that plug? And do you only run the two or 3

My buddy had the same problem with his 99-01 j2fab cobra alternator on turboed terminator. Only way to get it to charge was to bump up the idle. He couldn't find a smaller pulley.

Hmmm it did the same thing with the stock alternator that I replaced with the j2 fab unit. But you are right it does come back up in voltage with rpm increase

Ur alternator may be failing slowly. Mine was. I would bet its the wire leading to the battery. Just replace it.

There is a small plug that plugs into the back of the alternator. Make sure its in there securely cause it can vibrate out slightly but still have a connection but a lower voltage one. Worth checking out but I bet its ur wire.

I just opted for a 240 amp alternator which is a good idea imo with a Turbo car.

Battery is in the trunk none of the stock battery wiring is in the car any more. alternator wiring to the battery is 0 gauge and everything else is 00 gauge.

Pretty sure my j2fab is a 240 amp. it was the highest amp alternator they made at the time When I bought it a couple years ago. It’s plugged in good but I only have the two out side wires on the alternator plug wired and the center wire not connected to anything. Should that been wired to something also? It’s been a few years ago since I wired the car I can’t remember how I wired it exactly

Here is the wiring diagram you can bounce your harness against. Also how did you splice the new harness on, crimp or solder??? If the pulley ratio didnt change check the actual voltage output at the alternator when at idle and the at the trunk battery terminals.

I solder everything when I wire stuff everything thing is hooked up correctly and I verified that with a voltmeter even put a brand new battery in the car. This basically brand new j2 fabrication alternator is garbage. It’s gets crazy hot after running for 2-4 minutes it’s shot