I have a weird voltage drop when I give it almost half throttle, the battery voltage drops to 12. As soon as I let off, it returns to normal. It's not anything to do with the motion of the car, it will do it in park too. I've checked the wiring to the alt, everything looks good, any ideas?

 

You may have already found the problem (since this thread is 8 days old) but it sounds like your belt is loose.

 

could check the battery cables to see they have a loose
connection or other fault affected by movement of the
engine,or could be an internal fault in the alternator
such as out of round slip rings,worn brushes,broken
connection in the rotor,ETC.

 

I haven't found the problem yet, the belt is tight, its just a certain amount of throttle movement that causes it, at any engine speed or driving condition.

 

Is it causing a driveability issue? Have you verified the volt drop at the batt terminals with a DMM, maybe it's just the gauge that's dicky for w/ever reason.

 

It's not a drivability issue, I just know its not right, I haven't tried it with a volt meter, but the ecm is seeing the drop, it showdown up on the data stream.