If the inner skins are off...WHY don't you put in new wiring...? This is the time to modernize and improve safety overall. Check where the wire goes thru stringers and run grounds from all 12v
fixtures...at least check them well. Any good trailer shop will sell you a length of 7 wire to use.....then its all done new and you know actual layout.
"If it can't be reduced, reused, repaired, rebuilt, refurbished, refinished, resold, recycled or composted
then it should be restricted, redesigned or removed from production."