Arrow alt and gear
 

Arrow alternator trip on gear up
Maintenance baffled

Facilitation around the moving parts of the switches ? , dry lube , mud ,grass , gravel , ice , on the stop switch . If whatever was keeping the up switch from indicating up is no longer there . Foreign object substance lost when the gear was dropped again ?
Sign at my old AMO shop :
Answers $50
Correct answers $100
Dumb looks are still free

Could it be the regulator failing to reduce the alternator field when the pump load was stopped, the transiant rise in voltage tripping the over volt system.
But what has caused this to manifest after years of correct operation?

I don't have any aircraft specific knowledge but issues related to the stoppage/turning off of an electric motor are generally associated with the failure of the 'freewheel diode' that's part of the motor (or motor drive, in larger installations) and is there to stop transient overvoltage spikes by allowing the collapsing magnetic field to dissipate the electrical energy it generates into a loop rather than slamming up against an open circuit. (It's there to prevent the electrical version of water hammer.)

Googling that term (freewheel diode) and a bit of looking at the wiring diagram might help you out. Diodes can be tested with a multimeter. It may be part of the motor assembly or inside the motor.

Failing that, yes, voltage regulator failure, they do get old and fail...

Thanks for your comments, solenoids in aircraft often have diodes fitted but I havent seen it on motors, if a regulator change doesnt cure we'll try a beefy diode.
My regulator may also be faulty cos I'm feeling old and frail, or was that fail?