I tested the float switch, which I had just installed last season. It had no effect on the pump so I cut the wire to the pump and went off to West Marine for a new switch. Of course that new switch made no difference. I wasn't thinking clearly.
Later, I went off to the web to order a new pump. Of course Jabsco would have an exact replacement for a month, so I ordered a similar pump. I had a very good pre-sale experience with the folks at Neu Sporting Goods and am looking forward to a new pump.