At 11:36 AM 5/21/2010, Mike \"Rocket J Squirrel\" wrote:
>I may have to get an analog meter and connect it to various bits in the
>van to find where the voltage swing is highest. Anyone got a working
>Simpson 280?

I've got a very nice little Amprobe AM-1E (30k/vdc, taut band, fairly
fast movement) <http://www.tequipment.net/AmprobeAM-1E.asp >  Too bad
they're discontinued, but I found mine on the shelf at the local
appliance-parts depot for ~$80 a few years ago.  Of course having
gotten used to good digitals I get cranky when it's a quarter of a volt off...

But surely you have a scope?

>Before I dig deeper into this, can anyone tell me if this sounds like an
>alternator voltage regulator thing? It does not vary with engine rpm.

I've experienced this at various times with various vehicles (car,
boat, Vanagon?).  Never bothered to measure and always seemed to me
that it must be VR-related, but haven't thought beyond that.  If you
watch carefully I think you'll see it's not a step function, more
like a sine wave.

Yours,
d