on my '86 , it is mounted on the center firewall in the engine compartment. it usually has about three terminals , maybe 4x6 inches and looks like a heatsink for power transistors (sometimes). if you have to replace one, get two, they can be hard to find. the output wire from the alternatoe goes to one terminal (assuming an internal voltage regulator on a '92) the isolator splits this between batteries. one terminal for each battery. good idea to label which is coach and chassis battery very plainly so some mechanic doesn't screw it up when checking something. you may have some other safety diodes in the wiring somewhere . mine has something, i'm not sure (or can't remember) if it is diodes or inline circuit breakers. they are about an inch long. mine are mounted with two screws. these are not part of the isolator, but, could confuse you. they wont matter unless they blow like a fuse.