Imho, you can request the original parts to be replaced on your trailera d the labor charged commiserate with the troubleshooting and wiring repairs.
I don't think you can reasonably expect to be refunded the price AND keep the parts.
I do not believe you should be required to pay excessive labor to make up for the mistake.
You might make headway by offering to pay for the parts (new does have value, even if prematurely replaced), but request significant labor reduction.
It's easier to give concessions out of labor differential (profit) and accept break even, rather than paying out of pocket and allowing the customer to profit.
Good luck.