A couple months ago (when it started getting colder outside), I noticed while driving that the check gauges light was flickering on and off when the engine was running at or above 2000 rpm. I found out that the check gauges light only comes when either the battery voltage, oil pressure, or coolant temp. is above or below the normal operating range. I'm currently daily driving my 96 z28 and have also noticed that when the light would illuminate, my battery voltage gauge would drop lower (about 10-11 volts). Also when the gauge dropped and the check gauges light turned on, all of the lights on the car (headlights, interior lights, gauge cluster lights) go dim, and return to normal when the voltage gauge goes back to normal and the check gauges light turns off. I have also noticed that it only occurs when the temperature is below about 35 degrees F. I've done some tests and found out that the alternator output cable to the battery is good and the serpentine belt is not loose or slipping. I have a good feeling that there is something wrong with the alternator, but wanted to know if anyone else has run into this problem with the 4th gen f-bodies before I spend $150-200 on a new alternator.

 

See if your local parts store will test the alternator for you, that's what it sounds like. I had a similar experience with my LT1 Vette on a road trip. The alternator must have had a bad bearing that was momentarily hanging up, causing the dash warning light to keep flashing on and off, till it finally had enough and locked up. I was on the road out of state, so didn't have the luxury of giving it a proper autopsy.

 

Would they still test the alternator even if the check gauges light isn't illuminating at the time? Because it only happens when it is below about 35-40 degrees, and lately has been above that so it hasn't been illuminating.