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What the Heck

I have a 2000 Chevy Astro van, and I have this problem that no one seems to be able to figure out, let alone fix. Occasionally the car with have all the lights inside and outside the car start to “pulse”. The needle on the voltmeter will be noted to surge from the average just above 14 mid point on the dial on the meter face to over this in a pulsing motion, in time to the light pulsing. I have replaced the distributor cap, coil wire, and the car has been with the mechanic numerous times. His diagnostic equipment does not pinpoint the cause of this problem. Do you have any suggestions of what to try next?

Faulty (intermittent) ground?
If somethingets hot and expands and breaks ground circuit?

If bad alternator, I’d expecthe battery to fill in thelectrical “voids”.

Or something SHORTING. But I’d expect to smell it or see it.

Whatever is going on is cyclical, meaning your car is operating normally during some cycle and operating abnormally during another cycle. In this case the voltmeter surges to just above 14 volts.
This sounds like the voltage regulator. The headlights expecially would respond to increases/ decreases in voltage, and at night make for a pretty obvious symptom.
Your regulator should be inside the alternator, and you should just go ahead and replace the alernator.

I tried but was unable to find out if you have exterior or interior (inside the alternator) regulator. I think it’s internal in your car. If anyone knows better, hopefully he or she will say something. If not, replace the alternator.

This does not likely have anything to do with the ignition system.

Failing alternator, battery cable ends with scaled over contact surfaces, or a corroded junction terminal is what I would be checking first.

Is this a case of the inside lights being totally off and then they turn themselves on with a pulse effect? Can you explain the sympton again? I am thinking of a short to ground in the drivers electric seat (is it electric?) and a circuit breaker rather than a fuse opening and closing. We saw the short to ground in the late 90’s S-Blazer quite a bit (in the seat wiring).

In your description please include as much detail as you can, this is a time I need to hear a big story, not the short version. One other thing, has the engine cover been off lately? I ask because there are some wires that can be pinched between the engine cover and the van body.

Always check that the big nut holding the big cable at the starter is tight (this was a major problem on all GM trucks from your year).

Thanks for all the answers, I think replacing the alternator has got it done! Thanks again for all your help!