[geotrash]

Thanks for your quick help. I spent some time with an ohmmeter this morning checking grounds for the engine compartment and chassis, and all checked out fine.

Basically, I think it's either an alternator with a failing regulator that's causing the electrical system to pulse, or something is putting an uneven drain on the charging system, like the fuel pump surging. When the engine is running, the idler pulley on the serpentine belt is moving on the same cycle as the light pulses, indicating that the alternator is loading and unloading about once a second.

I think I'll go ahead and replace the alternator for starters, followed by the battery. If that doesn't do it, I'll start isolating systems looking for a short or unusual current drain patterns. If anyone is interested, I'll report back here with whatever I find.

Cheers,
Dave