08 xlt f350 fx4 Superduty....I think my truck had a slide in camper at some point before I bought it. Any idea what this wiring is for? I cannot find any information anywhere. 1 wire goes into the cab off that bell looking thing and the other stays outside and follows inside the frame rail and there is a harness inside the rear about a foot past where the fuel tank throat is. I havent seen what the end looks like because I am waiting for warm weather to take the bed liner out. Thanks
Directly from battery.

 

Looks like a trailer charge setup. It's what you would use to charge the battery in a camper, or a dump trailer that has a battery on it for the hydraulic system, anything like that.

That late of a model truck probably already has some of this type system already in it from the factory. But you need to have the documentation and be able to find it in the harness to hook it up. They probably found it easier and quicker to make their own. Looks like they did a decent job. The little square thing is a circuit breaker. The round can should be a continuous duty solenoid which sends power to charge the trailer battery only when the key is on.

 

Spot on, that's exactly what it is.

 

Thanks. I assumed it was but you know what happens when you assume things..lol This truck is 6 months new to me so I am trying to piece together a little history thru investigation. I'll just leave it alone until if and when I need it. Thanks again for the quick response.