The tail light wiring is inside the fender exposed directly to rocks and and moisture thron up by the tires. Not a good situation, but making covers is pretty simple.
First lay a dowel in the fender where you want the wires to route. Then cover the entire area with duct tape. Resins won’t stick to the duct tape so you can use it as a simple positive mold surface in areas where cosmetics aren’t important.
Once the duct tape is in place, lay a few layers of glass and wait for it to cure. Presto, instant custom fitted covers.