88 740 GLE Charging System???

[Flageek]

Will try to keep this short and to the point.. Car would whine when lights turned on, told alt was going.. Car would not start, bench tested alt, it was bad.. Was a Bosch alt in car took the cheap route and replaced with alt from Autozone. Installed hooked up battery, instantly charging light in dash comes on (key not in ign) Friend who installed says well its a dummy light lets see if car starts.. Car starts runs like a charm. Drive to work, home and quick trip to store car dies.. Jump car starts up.. Take alt out because am told its faulty (5 diff men who know cars???) Autozone benchtested said its fine but does replace with another, same problem.. Call around to local garages they say its a wiring harness, 1600 to fix.. Any suggestions as This car had no other problems prior. Am I grasping to save this car? This alt is showing 12.1 volts while car is running I have read at several boards it should be 13.5-14.5 is this the problem or are there deep rooted issues? Why would a dash light come on without key in ign? Wheres the power coming from?

Thanks for any help..

A geek who loves her volvo...