95 Z71 wiring problem??
 

I just bought a 95' Z71 w/ 350 engine. I thought the alternator was gone out in it. I can jump it off just fine, but when I unhook the battery the truck dies!! Alternator right???? Thats what I thought, i took mine off and had it tested at Orielly's. It passed, but I bought a new one just in case. Took the new one home and put it on. Same problem, jumped off fine, unhooked battery and truck died. So now Im thinking that its either my wire running from alternator to ECM board, or the ECM board itself is bad. My question is, how do I find out exactly which pin hole on the ecm board is the one for my alternator??? I dont want to buy a new ECM board if its just the wire shorted out. Any help would be appreciated, i like the truck but feel like I got screwed on this deal.

It is not a good idea to disconnect the battery while the engine is running. This sends a voltage spike through the system and could damage some of the electronics. The best way to check the alternator is to put a volt meter on the battery with the engine running and if you get around 14 volts then it is working. There may already be some damage to the ECM.

Is there any way to specifically test the wire from the alternator to the ecm board? If i knew excatly which pin hole it was on the wire harness i can test it, but without knowing which one it is, i'll just be shooting in the dark.