my f-ing electrical system

[ChrisCantSkate]

well, ive been trying and trying to fix my alternator problem. im 100% sure the alternator works, and im 99% sure its something electrical, which is causing my alternator not to charge the battery. now there are 4 wires on the harness going into the alternator(not counting the big wire you bolt down). the black/yellow and the white/green are supposta read ~12v when the ignition is on, the other 2, im not sure about. the black/yellow tested out fine but the white/green is pulling ~0.15v at the alternator harness and 3 inches from the ECU. in my manual it says to check for shorts in the wire but its basically impossible to check the wire since its wrapped up in the engine harness except for about 6 inches on each side. my other thought was a missing ground but i couldnt find one i forgot. any ideas what could be causing the wire not to be getting/reciving any power.