That's the problem there IS NO where else. There was a big argument on here couple weeks ago........you CAN use a fuel pump style (multiterminal) oil pressure switch, but the thing is, since the bulkhead is a bit flakey anyway, cutting the IGN1 wire and inserting a relay solves several issues:
1....It gets rid of voltage drop to the regulator which causes overvoltage/ overcharging
2...It gets rid of the entire issue of poor connections/ voltage drop to the alternator field, the ignition system, and of course.......your choke.
3...If relieves draw and stress on that bulkhead circuit, and including the igntion switch terminals.