When I start up my '94, I notice that the lights on the car (headlights, dash lights, interior lights, tail lamps, etc.) fluctuate in brightness. They slightly dim and brighten very quickly, maybe 10-15 times per second or faster. This is also accompanied by the alternator meter in the dash also very slightly bouncing along at the same time, always in tune with the lights dimming and brightening. This continues anywhere from, as far as I've observed, 10 to 25+ minutes of normal driving, and then ceases as I've driven it for a good amount of time. I had the alternator checked out today, and the test showed that it was working fine.

As far as the car, I recently replaced the battery, replacing my old Optima RedTop with a new one. The OptiSpark has been replaced in the past 10k miles, and the plug wires have been replaced in the past 20k miles. The car has just over 60k miles. It's an LT1. I haven't disconnected any ground wires, although one may have come loose or corroded without my knowledge.

Any thoughts?

 

Just a few hints, regarding troubleshooting:

For a fluctuating voltage problem, an analog volt meter will usually work a lot better than a digital one (and fortunately they are among the cheapest ones you can buy at Radio Shack). You will need the FSM and especially the electrical section.

Pulling fuses one at a time and watching the voltage is probably the most direct way of narrowing it down, assuming it is NOT the regulator or power source related.

Sometimes pulling fuses is not an option, especially if the circuits are related to the computer, fuel pump, etc. In that case, troubleshooting becomes a little more involved, but still pretty straight forward:

Pull the fuses on any non-essential circuits to at least narrow which essential circuits may be involved.

Now, if the regulator is the source of the problem, the range of the measured fluctuation will be more or less the same throughout the rest of the network. However, if the cause is not the regulator, the range of fluctuation will increase as you move away from the battery/alternator toward the source of the load causing the fluctuation, unless the cause is very close to the battery. However, fluctuation ranges of circuits that are parallel to the affected circuit will not increase, but remain about the same: You're looking for the circuit where the fluctuation range is increasing.

Hope this helps.

P.

 

The voltage regulator in your alternator is oscillating causing the alternator output voltage to wiggle. Engine idling with lights flickering, unplug the alternator and if the flickering stops, this is proof the voltage regulator is oscillating. You can replace the voltage regulator or the entire alternator. The lowest cost way if you don't want to do the work is to find an auto electrical repair shop and have them replace the voltage regulator in the alternator.

 

Doh!! Good point. (I think I just had a "palm to the forehead" slap!!) I didn't think of that procedure, but you're spot on; it would eliminate the (most likely) cause right off the bat!! If that isn't it (but I'm betting it is), then it will be time to go pulling fuses and pokin' around with a VOM. Good catch!

P.

 

Had a guy at work with that problem and since we had a portable 12v powered oscilloscope, this unbeliever insisted that at lunch I show him the waveform across the battery even though unplugging the alternator stopped the flicker. The waveform was a good sinewave. Had to rub his nose in it!

 

Any idea of the cost of parts? Is the process involved, or pretty easy? I don't have a huge set of tools, but I can do the basic stuff on my own. If not doing it myself, how much would something like that generally run? Thanks for the reply, tracking down electrical gremlins can be frustrating.