Hello NEWBIE and welcome,
I have some experience in replacing a wiring harness i done mine a 77 Luv and its pretty straight forward & easy, as most the wires are in 1 bundle w/ the fuse block except some smaller harness which branch off..since your harness is already compromised I would take that route i believe 78 started the shorter fuse block as 77 still has the long one so 78 to i'm not sure 80 maybe 81 NOT SURE but definitely after 77..
I see your up in Washington and I just checked on line in Pick n Pull. a 78 Luv is at the Lynnwood, WA 98037 yard (check
http://www.picknpull. com ) it was put in the yard on Jul 10, 2015. & w/ any luck you'll find your wires harness there
the next closes luv in a PnP has a 79 but is in Oregon..
There's 5 PnP's in Washington so if not check other yards Craigslist or even ask in this site & fb luv groups and keep checking back to the site as once in a yard its a mad dash to see who get there first
as far as you malfunction in starting ..I'd start w/ the harness maybe its a short and will be taken care of w/ replacing it.
Good Luck w/ your repairs...Peace