M42 not holding charge HALP

[MF DOOM]

Just finished my m42 turbo and it wont hold a charge. Brand new alternator, tested and passed. New battery, getting anywhere from 10.5-11.5 volts when the car isnt running. the alt seems to be grounding fine but im going to run an independent ground to the chassis. When i start the car, have to jump it, the volt reading i was getting at the battery dropped steady and quickly from 11.5 to 7.2 where it stayed in that area till the car died. Any ideas?

EDIT: Can someone get me a picture of how number 8 in this diagram is hooked up? If i have something wrong here could that be doing this? im also thinking the wire between the starter and alternator

[VANOS714]

check your alternator ground cable, might be old and needs to be replaced.

[MF DOOM]

The alternator grounds through the engine.. That was my first thought as well. Any one else? Any help at all? Maybe a solenoid stuck open? might have it tested.

[Dj Buttchug]

check the battery cable ground in the trunk. make sure its tight and you actually have a ground there.

[MF DOOM]

Checked it. Cleaned it up. Battery ground is good. The car dies as soon as i pull the battery ground. i have voltage at both of the alternator wires and its grounding fine. Does anyone know where the small wire on the alternator goes?

[jlevie]

The small wire to the alternator is the exciter. Without exciter current the alternator won't charge.

[MF DOOM]

Just chased down where it goes on my old harness. Ive got voltage there so that shouldnt be it, right? going to check the continuity of the wires. For the exciter wire, should i have voltage at the pin on the fuse box plug?

[MF DOOM]

Added a ground wire from alternator to chassis. problem solved.

[VANOS714]

Added a ground wire from alternator to chassis. problem solved.

Had the exact problem :)