78 911 Electrical Problem

[Robert Gomez]

Got the RED light on the bottom center on my Oil Temperature / Oil Pressure Gauge...initial start up light is on relatively bright n steady...when driving or greater than idle revs light is very very dim...is it the alternator / voltage regulator???

[jmohn]

Probably.
I think the top light is oil pressure and bottom light is the charging system. If the charging system light is illuminating, any amount, while the engine is running (at 1500-2000 rpm or better) there's a problem with any of the following: battery, alternator, voltage regulator (original was external on a '79) or any of the wiring connections that make-up the charging circuit. You could start trouble-shooting by checking the charging rate at the battery (engine running) - you should have a minimum of about 13.1 volts. If not, clean and re-install battery connections, retest, then check all ground connections and retest, if external voltage regulator - remove clean points and contacts reinstall and test, then check positive cables (typically red) and connections, and retest, and finally test the alternator.

You could do these tests in any order you choose, this would be mine.

Good luck,

Jerry M
'78 SC