GMC Repair: Surging Headlights and Dash Lights, pontiac trans sport, 3800 engine

Question
I have had a 1992 Pontiac Trans Sport since new.  (3800 engine)  I had the original alternator rebuilt about 10,000 km ago.  It needed bearings and brushes.  The rebuilt alternator had no problems but I recently noticed that the headlights and dash lights (as well as the radio display) will surge slightly.  (You might use the term pulsating instead of surging.)  It does not seem to depend on engine speed.  The engine can speed up and the surging frequency does not increase.  The surging may stop after the engine is revved slightly.  However, the lights usually keep surging after the revving.  At times, the surging does not exist at all.  The lights stay lit and do not "surge".  I took the alternator back to the shop that rebuilt it.  The tech put the alternator on the test bench and everything tested fine.  The output was up to specs.  He then idled down the alternator and the test bulb he put on it glowed normally without surging.  I have checked some ground areas under the hood but nothing changed.  The surging usually occurs after start-up and I notice it backing out of a dark garage.  However, the surging can be noticed sometimes when I drive into the garage after the vehicle is warmed up.  I appreciate your advice.

Answer
Hi
Just to clarify, the surging pertains ONLY to the lights, and not the actual idle quality of the van's engine, correct?
If so, sorry to say,  the ONLY times I have seen this it has ALWAYS been the Alternator.
(Not saying anything wrong about the rebuild or the tech.)
The bulb he was using was hooked directly to the alternator.
Your bulbs that are surging are being lit along with other electrical items on at that time as well as being fused and like the radio, is actually being lit be the device, not directly by the Alternator.
Also taking into consideration the age of your van, there may be some resistance in some of the realted wiring,along with the power, grounds, etc....that may also explain this.  The wiring is also 15 years old now, it too has been through alot. You can/could check your battery connections, check the cables. Make sure they clean and tight. Make sure battery is fully charged, and see if the lights still flicker. A Slightly weak battery will take a little extra current from the alternator.
I hope this helps.
Just advise from experience.
Good Luck
Paul