Don, et al,

 

As I promised, I performed pump experiments with the following setup:

 

 

All I had to do was watch the bubbles (this is not a Lawrence Welk device).

 

I used lighter jumpers so that they would burn up instead of other possibilities (note, no breaker/fuse).

 

The up and down (hi and lo) pump operations were checked several times for a few seconds each (the wires did warm up).  Also, note that the pump body is ground (battery -).

 

Several times I applied positive voltage to both wires simultaneously and the pump would not run.  I only held this for a few seconds to not over heat the wires.

 

Then, at least six sequential connections to both wires were made separated by a second or so (Dn-Up, Up-Dn) and all but one resulted in the pump running primarily in the down direction with foaming visible in the up direction tube.

 

Although this doesn't quite explain why your gear did not stay down and locked, it does show that power can be supplied to the pump on both the down and up wires without popping the breaker.  Your pump may have acted differently over the long period of time from base to touchdown.  What happened to the pump in your situation might be determined if those discarded parts are still around.  I've got everything that ever broke on my airplanes, some of the things make great paper weights.

 

I know you can't see detail on the battery positive terminal, but the contact points where I touched the jumpers did blacken up quite a bit.  It sure would be interesting to look at the relay contacts for burning or welding.