I have an FLHPI 2003, went to the Black Hills for the weekend. Rode part way home in the dark. Noticed that the headlight would slowly get dim and the brighten back up. never to the point of not being able to see the road but enough to know that it was happen. Seams to be cycling to the count of 20 so I don't think it's a ground problem. Thinkin along the lines of voltage regulator. I will get the service manual out tomorrow and do some checking. Is there something I'm overlooking ? I had about 150 miles to mull this over as I was crossing my fingers and toes hoping I would make it home before it got worse.

 

Sure does sound like a voltage regulator type problem....let us know what ya find.

 

Check the voltage with a meter first.

With the motor running at 1200 + rpm you should see voltage of over 13 volts DC at the battery ( if more than 14.8 you may have a regulator problem).

If voltage is stable and in proper range, look at lighting grounds.
Stuff gets corroded.

Loosen the ground connections, brighten with scotchbrite pad, tighten up again. And look at the headlight plug, poor connections cause heat and can melt it, the contact tangs can be pulled out of the plastic housing and cleaned

If you had serious charging problems it would likely manifest in drivability problems, the fuel pump, engine control and ignition systems all need voltage in the proper range.

MK