On my 06 Expedition, the electrical system goes up & down while driving. The headlights go dim, fan slows, wipers goes slow for about 10 sec., then goes back to normal for about 2-3 minutes and repeats cycle. Does not do while in park/idle. Gauges do not fluctuate. Any suggestions?

 

Try cleaning the battery teminals.

Do you have any auxilary items (like a high powered stereo) that require extra electrical juice?

 

Nothing extra added. Factory options, ex: fogs, rear heater, etc.
Will try cleaing battery posts.
Thanks.