On mine I use a Ford type starter solenoid in the trunk since I ran my starter cable under my carpet I did not want it hot all the time so its only hot when cranking as I have it going thru the solenoid. The smaller red wire is my 12 volt feed which is the wire my cutout switch controls as it goes to the starter relay on the firewall where the car picks up it hot 12 volt feed to the fuse box , ign switch , headlite switch and so on. I have a 70 am fuse with eyelets on it on the red wire as its bolted to the battery cable end and then hooked to the wire. The black wire is my alt output. I like the idea of putting the field circuit on a relay that would kill the field when you turn the kill switch off and stop the charging system from working. That would work as long as the relay control turns the relay off when the cutout switch is turned off. Ron