??? Easiest way is to just hook to the two large bare terminals on the starter relay. Most the time I don't even use a switch, just a screwdriver, pliers, "any other" piece of metal I have handy
MAKE DARN SURE the trans is in park or neutral. If it fires, it will "go."
(If I live long enough to get my own car back together, this will be more difficult, LOL. There will be no starter relay "under the hood.")
