Phil,
Not sure where the power comes from. If you cannot find the source of the problem, with a reasonable amount of effort, and other switches on the same panel have power you should be able to rewire from one of those as a source. The trigger for the relay is low current, less than an amp, probably around 200MA. On my older Contessa the switch panel did jumper the + harness from switch to switch as a relay trigger power source. The other source you could use is the wire that goes to the accessory 12v recepticle using an inline 1 amp fuse feeding the docking light switch. Hope this helps.
Later Ed