I put a 20A auto-resetting breaker on each headlight relay, per kit instructions.
Mine feed off that terminal block on the fender. Not sure if your guy didn't use breakers or just went around that terminal.
Kinda sounds like your PO just re-used the wires once he got them to stop smoking, so they corroded where the insulation was compromised. Zero chance of that biting anyone in the ass down the road
