My 1988 744 alternator light comes on cold mornings. The gauges are dead when the light comes on BUT my temp gauge starts working (usually dead temp gauge when gauges are working). About a mile down the road, the light goes out and gauges starts working. I have tightened the ground screws at the alternator and at the battery-to-chassis ground. I cannot find fault when temp is in the 50's or higher. I drive 3.6 miles to work and the car has performed flawless ly otherwise. Great heated driver/passenger seats when cold.

 

This can be a variety of things but what I think of are 1. Failing ignition switch (the electric portion that fits to the back side of the actual key lock. 2. A bad ground on the cluster itself or where the cluster wiring grounds.

 

My mechanic said that replacing the voltage regulator would fix it. There are two carbon brushes. One was really short and was catching if I pushed it in. So for $35 I am a happy camper.

Now for the struts that hold the trunk up. I was replacing tail lights and the lid dropped on my hands OUCH so it's time to replace the gas struts.

Update: morning frost on car, 31 degrees were the combination that the alternator light comes on. Started the car and drove to work. Alternator light stayed off and worked fine.

Now, on with the temp gauge not working.

 

Temp gauge usually is the connector on the sensor rotten, or the compensation board behind the cluster (which can be fudged).