I have a similar problem with my 04 WRX
When i turn on the engine the voltage goes to 14,1v, and after some seconds goes to 12,5-12,7 in idle
If i turn on the light, the AC or other , the voltage goes to 14,5
If i rev, the voltage remain stable to 12,5 or 14,5(with something turned on)
I don't think this is normal, any suggestions?
I've already changed the alternator with another toke from a junkyard
Do you know where the ground cable are?
Thx