JSracing

Replaced the alternator because the battery wasn't charging. Now the alternator is working, measuring 15 volts at the rear of the alternator but it's not making it to the battery. Still measure battery voltage only at the battery. Has anyone got wiring diagram ? Thanks.

C5 Diag

Sounds like you need to get down to the starter solenoid where the B+ from the alternator and the B+ from the battery come together…if you have a bad connection there the battery will not charge…if you have a DVOM place one lead on battery positive and the other on the alternator B+….you should only see about .1 to .2 volts or so…do the same from battery negative to the alternator case…it’s a good idea to fill out your profile with model year, mods, tune etc.

Dano523

To add, if a wet sump motor, the ground side of the battery cable goes to the engine block, which could be loose as well.

So check your voltage at the battery terminal,
then use the engine fuse box terminal as your positive source, reach across and use your alternator body as the negative source, and if you do have close to the same voltage as the alternator output on the later, is the grounding bolt on the side of the engine block the problem.

Note, in this photo, the solenoid connection point for the battery to alternator cables has cracked off, but you can see the ground terminal bolt just above the starter.


On a dry sump motor that the battery is in the back, the ground off the battery cable is about 3" forward on the battery to the chassis rail, while you still have a grounding strap in the same place to the motor as well, so the later test still works to check for grounding problem.