Several years ago I replaced my standard headlamp bulbs with 100w bulbs. It seems that whenever I drive the car with the headlights on and come to a stop my voltage gauge goes well into discharge territory. Once I get moving the gauge returns to the charging side. This is really a problem in stop and go traffic with the headlights on. The alternator is a rebuilt Bosch unit standard for 914 and was replaced about 5 years ago. I'm thinking of replacing the headlamps with an HID set-up to reduce the load. Is this an alternator problem? If I run the fog lamps or put on the turn signal while stopping, the system discharges. Thoughts are welcome.

Try replacing the voltage regulator.

Dave

If it's like VW's, some voltage regulators are adjustable. I just did that operation on a beetle.

If it's mounted in the console that is totally normal. Check the voltage w/ a VOM directly on the battery posts to verify. It should at least throw a charge above 1500rpm.

alternator belt tension?

Your voltage gauge in you center console is fed through the brake circuit and voltage will show a drop when ever brakes are applied. Not a great design and you can change the voltmeters source. At least it lets you know the brake lights are working.

Always check your ground strap. It's the easiest solution and hopefully it's it.