Anything is possible - and certainly I reserve the right to be wrong - but, on Page 8-163, the '89 FSM describes the oil pressure gauge and the oil pressure gauge unit as "Bimetal type". I'm not sure if the oil gauge circuit is voltage-limited - but I'm assuming any and all of the bimetal gauge units are, since over-voltage would wreck them. I haven't checked the schematic, though. I have taken apart a gauge cluster and found the voltage limiting circuit, but don't remember if it protected all of the gauges or only the fuel and temperature gauges.

The fuel gauge bimetal and maybe the ECT gauge bimetal certainly can be damaged by alternator voltage spikes, so I would think the oil pressure gauge might also be susceptible..... but I'm not certain of that.

In any event, the oil pressure gauge unit can be checked with an ohmmeter across the terminals - the standard value is 50 ohms.

Frank