When doing a timing Belt job in my 1987 Porsche 928, we cleaned up the engine bay and made sure the electrical loom associated with T18 (an under the hood terminal connector) was routed and secured properly.
While doing so, we came across a modification by the previous owner consisting of a small bulb attached to T18 pin 1 and ground, it was tucked into a short piece of rubber hose to protect it from moisture, etc.
Pin 1 goes to the alternator's exciter terminal, assuming it was there for ease of diagnostics(?) we removed and discarded it, unfortunately.
Now when we start the car the voltage gauge reads barely 10 volts, the alternator light goes out as it should, BUT the oil pressure warning light starts to flash, despite plenty of oil, and the gauge reading full pressure.
As soon as we blip the throttle, or slowly increase the RPM to about 1800, both problems go away.
If the RPM returns to idle, the problem DOES NOT re-occur.
However, turning off and starting again several times, causes the problem to re-occur.
Any thoughts on what is causing this, perhaps you've heard of it before?