The interior wiring is hacked up and spliced They used household twist connectors. They spliced into the wiring and used a toggle switch for the dash lights. Engine harness isn't any better I feel safer just replacing it all
Easiest may be putting a wanted ad up for '75 engine & body wiring harness in good condition.
Otherwise spend as much time as needed to figure out what different between the years and options.
I'd look at '73 as well as '74 since niether 73 or 75 have the interlock.
For that, my suggestion is to start with a few critical items.
1. Is the bulkhead connector in the same location and fit in the same opening?
2. Is the starter relay, ECU and dash switches in the same location?
Then compare feeds and out of the steering column connector.
