Enblethen,
Thanks very much. One of the photos you linked to looks almost exactly like this device, so it looks like it is a circuit breaker. One of the things that caused me to hesitate in thinking it was a circuit breaker is the location (outside, fairly accessible to weather and road splash-up). Always figured circuit beakers were kept in closed, dry locations.
Once again, thanks for your help.
p.s. travel a lot from Vancouver BC to Denver Co along I-90 and quite like the Moses Lake and surrounding area.
Marv