This is probably the same for all Dodge 2500's as it looks like the fuse
box is designed for multiple applications.
My trailer power at the 7-prong plug is always hot. It should only be on
when the engine is running. Under the hood on the driver's side (USA),
there is a box with fuses and relays where the main power distribution
is. There is a fuse marked trailer power and if I pull that the trailer
power goes dead. There is also a relay marked trailer power and if I
pull that the trailer still has power.
It should go on with the engine to charge the trailer batteries and go
off when the engine is shut down to prevent draining the truck batteries
when the trailer (in this case a slide-in camper) is parked.
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.
Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here.
All logos and trade names are the property of their respective owners.