'86 Nissan D-21 charging issue

[lateniteproductions]

i have an 86 hardbody that when the batt is unhooked, the truck will die. i have taken the alt off and had it tested, but it passed. so i bought another one as a just-in-case measure and it still will die with it installed. there was a capacitor that was on the back of the factory alt, but when i removed it the first time, i noticed that the wire was broke coming out of the capacitor. dont know if it is important or not?!?!
i have also ran a wire directly from bat terminal on the alt to the batt with no luck. when running, a volt meter reeds between 11.7v and 12.4v. i have racked my brain and now need help. Thanks in advance

jeremy

 

[doctordick]

The capacitor on the back is just for radio noise suppression (can also affect ECM). It needs to be there, but won't effect charging unless it shorts at which point all of the smoke leaks out. Does the vehicle have an external voltage regulator? 11.5v to 12.5v would be normal for a fully charged battery, but you should see around 14.4v while running if everything is OK.