Was it just the ammeter flickering, or all the lights too? This is number two alternator I have installed, don't think it is the problem. I plan on going through the charging system this winter. Thanks for input..
My ammeter flickered slowly when the engine was close to idle speed. Rev it up and it stayed steady. The lights did not flicker. In the winter when the heater fan was on high and the headlights were on, the ammeter showed negative 5 - 10 amps. And the lights would dim when at a stoplight. As soon as I took off, the ammeter went positive and the lights got bright.
If not already said, the firewall/bulkhead is a place where corrosion can cause a voltage drop.