I have had to trace a fault on my Enfield. The starter solenoid had failed. In checking out various readings I discovered that when the starter solenoid switches off, the collapsing magnetic field induces over 25 volts across the battery, and everything connected to it. (This voltage is just a momentary spike).
I would suggest that you never leave a phone, GPS etc. connected to the bikes power when you operate the starter motor.

PS, do not pressure wash Enfield starter solenoids either

I've had Garmin GPS units hard wired to the battery for a long time on an R1150GS without any issues, did the same on the 950SE recently. I also know of a few customers who've wired Autocoms etc direct to the battery with no problems for years.

Is it possible that your issue is caused by the jet washing incident you allude to or the fact that it's an Enfield?

Does Enfield still power the headlight straight off the AC supply? I had GPS issues with my bullet and eventually concluded the whole system was upset by the headlight having a direct AC connection but sharing the earth with DC circuits. You'd get earths that weren't at zero volts depending how far they were from the headlight connection. Some places you had 13V others 10.

GPS and Intercoms should have surge protection circuits, but typically these only work to 18V.

Andy

I dont know. I have never measured voltages on a starter solenoid before. In this case the solenoid was activating, but not passing current to the starter motor, maybe normally the starter motor absorbs it ?
Coincidentally, I had to buy a new mobile phone last week (samsung). Its' instructions say not to start the engine with the car charger connected to the phone and car.
The new solenoid is hermetically sealed, unlike its predecessor.

I measured the voltage wityh a digital voltmeter, so it was only a sample, I expect the peak to have been higher.
The Enfield uses a 200 watt three phase alternator which is wired directly to an electronic charger/voltage regulator. Everthing runs off DC/battery. There is a separate coil on the stator which is used to trigger the ignition circuit.