My 91 is having a charging issue, sometimes the Alt. is charging, sometimes it's not. In my experience an alternator is either good or bad. I have heard that the ECU somehow controls the VR, could this cause my symptoms? I think I have an ECU issue anyway, my fuel pump won't run unless I jump across the relay and I know that is controlled by the ECU.
Thanks.

 

How are those cables? Be my first suspect. Bad grounds can cause every electrical problem.