I’ve never had that problem, and I’ve probably had five different trailers I’ve towed over the years and two different boats. The only one I’ve had a direct battery connection to was a seven pin for a trailer with brakes. So I’m confused why he would have a four pin with a direct battery connect.No. The hot wire is to power the trailer light relay. There isn't enough amperage at the vehicle lights to power the trailer lights. Additional amperage draw on the taillight circuit will (probably) blow a fuse, throw a code, or both.
I’ve never used a battery wire on a four pin connector. Never blown a fuse or set any codes. In fact I’ve never heard of setting a code for a blown fuse on a turn signal. If you connect to the battery where does the other wire go? Four wire pin has four wires. Ground. Left turn signal. Right turn signal. Brake lights.So if I have zero use for trailer brakes I should be ok using the harness without the wire to the battery?
I'd run the wire either inside or outside. I don't plan on burying my Wrangler past it's axles so I ran it high underneath in a matter of minutes. I've added a similar harness to Ford and Mazda sedans I've owned without ever having issues. You can be safe and run it inside but I'd recommend running a separate wire.From what I have been able to find myself and what eTrailer recommends, there is only one style harness available for the JL/JLU. They all have the the wire to the battery. I’m going to buy the harness and try it without the extra run to the battery. If all is well, great. If not, I’ll take the time to run the wire.