Describe your alternator. There is only one model that ever used an internal voltage regulator and that was a Mitsubishi alternator on the Mitsubishi-built 2.6L four cylinder used through the '86 model year.
1990 is right in the middle of when they began switching the field current from the automatic shutdown (ASD) relay instead of the ignition switch, so to be safe, you should probably have the engine running when taking voltage readings. You should have a small black plastic block in the middle on the back of the alternator housing. There will be two tabs coming out of it and attached with very small nuts. Measure the voltages on those two nuts, the fat output wire, and right on the housing. The voltmeter's negative probe must be grounded to the battery negative post or the engine block, not on the alternator. Those four readings will tell us where to go next.
Saturday, January 8th, 2011 AT 6:31 AM