thanks for all of the suggestions.  consensus seems to be that i have a
grounded wire/loose connector somewhere, which i'll check out,
although that might not explain the fact that the light seems to flicker with
the speed of the engine (no buzzer).  the other possible cause is a
clogged sender, fwiw the oil was changed 400 miles ago, and this is on
an engine with about 1000 miles on a rebuild.  in any case, the thing
hasn't come on in a couple of days, so i'll check the wiring and leave it at
that for now.

thanks again, matthew