As best as I can tell The facts:  The high pressure switch was fused or
shorted in the on position after the accident. It must have happened as I was
landing, The gear was coming up. The inboard gear doors were still open and
torn off. The gear was undamaged.  I was watching the asphalt coming up in
these last few seconds and not my lights. There were definitely 3 green on
base and all the noise and drag that accompany 3 down. How the switch happened
to close (and remain closed) at the time of landing, I don't know. I had no
opportunity to do the emergency gear extension. I have since redone all of the
relays and added the diode protection as indicated in the SB.

Don,

 

That analysis doesn't sound quite right.  Even if the high pressure switch fused or shorted, there is no power to the pump unless the relay was also selected from power thru either the gear switch or the up relay never came open when you selected the gear down switch.  The pressure switch is wired in series with the gear switch and the appropriate relay coil.  In fact, the opposite pressure switch contacts are closed - up if gear down selected or down if gear up is selected - as soon as the pressure drops below the contact opening pressure.  I.E. Both pressure switches are closed during gear transition with the gear switch selecting which circuit sees power directed to the appropriate relay coil.  So......

 

Did you disassemble the up relay?  Did you find it stuck?  Or, maybe, did you check across the contactor points with an ohm meter before you discarded it and was there continuity?

 

Did you do extended "master switch on" electrical system testing without pulling the relay circuit breaker and the gear switch was in the up position?  Had you flown awhile with the motor power breaker pulled but the relay breaker was not pulled?  These actions will ultimately fail an intermittent relay or make it "sticky". The usual reason for pulling the motor breaker in flight is to eliminate frequent pump operations because of a slight system pressure leak down.

 

I have analyzed numerous hydraulic problems and many of them have been caused by intermittent relay failures after the relay was powered for extended periods since the relay breaker was not pulled when the motor breaker was pulled and as the pressure leaked down a relay was selected, depending on the gear switch position, with no panel light indication.  This is why one should wire the relay breaker/fuse after the motor breaker, just pull the relay breaker to remove power from the relays or make sure to always pull both breakers.

 

Even though the diode on the relay coil is a good idea, it will not solve the kind of problem you had.

 

BTW, before my first fight while the plane was on jacks and during a long electrical system check where I had the motor breaker pulled but not the relay breaker, I managed to freeze the down relay in the closed position by melting the coil winding goop that then held the solenoid core.  The next time I tested the gear up function, both relays were then closed and the motor ran although I can't remember which way it was pumping.  I found the relay details in a CSI style post mortem.  Now my relay power automotive fuse is wired after the motor breaker so that pulling the motor breaker removes all the power from the gear system - all the power.