Battery Disconnect with relay up front

The strategy of a 4 post (DPST) switch is to kill the ignition so that the alternator cannot continue to power the engine

With the disconnect hooked in the battery main line to the big posts of the switch, run a pair of no 14 or 16 wires from the two small switch contacts to "up front

"Break" the output of the ignition switch coming out of the bulkhead, connect the switch output to one of your two no 14's going to the disconnect. Take the remaining no14 coming back up front to one of the coil connection of your relay, and ground the other relay terminal, or, run it off to a grounded anti-theft switch.

Feed one of the switch contacts with appropriate fuse from the starter relay or your main junction. Run the cold side contact off to your ignition feed..........the one you cut in the first place

If you use a "continuous duty solenoid" or other heavy duty relay you can use this to feed you pump(s), ignition, alternator field/ regulator, and electric fans.

Run your big battery cable "up front" and either hook it to the starter post, to an aftermarket junction post, or to the starter relay post. Run a no4 jumper from there to the starter