Beware the previous owner, boat yard "electricians", professional qualified electricians and home brewed electrical work...
Nobody can be trusted.
Wires attached here, there and everywhere...
I've seen an 8V71 diesel started via a poorly placed little 16 gauge wire. Complicated Command Vehicle situation, multiple battery banks, multiple circuits, a pair of generators, split shore power... and one little wire incorrectly run between the two sides... Pull the battery switch, push the start button and vroom!
EVERY wire needs to be assuredly connected, and protected, where it should be.