Lot simpler to cut the "long wire" and install a weatherproof plug so you can switch out the old rectifier and put in the backup. BTW that wire is always HOT even with the key off so take care.
Sentence 2, no problem: I am paranoid about electrical stuff so always disconnect the battery before trying anything clever, or even something stupid.
Sentence 1: can you give a bit more detail on that? I have all manner of things for cutting the long wire, but what about this weatherproof plug? To be installed where? To plug into what?
