2001 Dodge 2500 CTD wiring for trailer power

I'd wire the charging circuit to the camper battery through a constant duty solenoid, triggered from the ignition. You could run the trigger wire through a dash mounted toggle switch so you can keep that circuit turned off when you remove the camper, or don't want it to charge. Constant duty solenoid:

Believe it or not, that's the way it comes wired from the factory. The relay is for the running lights, and is triggered by the headlamp switch. It's powered off the same fuse (fuse #8, 40A) that supplies constant power to the 7-pin connector, but split at a connector inside the PDC. I agree it's a bad design - I guess the thinking is that when you park, you'd disconnect the trailer power.

If you want it to operate the way you state (switched by the ignition), find ther red/orange wire leaving the PDC, (double-check that you've got the right wire with a voltmeter, then pull the fuse and make sure you lose voltage on the wire), and cut it. Put a 30A relay (get it with a corresponding relay socket - makes wiring much easier) inline, with the hot side going to terminal 30 of the relay, and the downstream side going to terminal #87. Ground terminal 85, and run terminal #86 to something that's hot with the ignition on. You can run a wire into the cab and tap into the ignition switch wiring, or you can tap into a "hot only when ignition on" relay in the PDC. The fuel pump output is a good choice - remember, you're only powering the electromagnet in the relay - a very low current draw.

Tom, Thanks a lot! That sounds like exactly the information I need! I was planning to do a relay thing but you have pointed me in the right direction. I will do some tests to verify I have the right wire and that I find one that goes on and off with the key.

Well, if it was a trailer, I might (or might not) disconnect when parked, but this is a camper (slide-in) so there is no reason to disconnect except of course to remedy the bad design in wiring.

Charles