I'd like to install a solenoid under the hood to charge my large RV trailer batteries, is there a good safe place to get accessory power (when the key is on) under the hood to activate the solenoid?
These batteries are quite large and will get drawn down alot at times, I don't feel comfortable charging them though the factory wiring harness going to the rear of my 05 3500.

 

I considered doing something on the same lines that you are, instead I installed a few wolar panels on the roof of my RV. I have not had any problems with batteries/power in the RV since.

CD

 

I just finished the same job on my truck.
I wanted a plug in the back for my slide-in camper that didn't have constant power.
I loomed up a 18g trigger wire and a 10g power wire that I run from the battery along the frame rail and zip tied it to the stock harness all the way to the back.
The battery end of the 10g I put a waterproof fuse holder in with a 30a fuse.
The trigger wire I ran into the cab to my ignition source relay I already installed ( I have a relay I hooked up to ignition source that I tap into for all my keyed power requirements)
At the back I mounted a Ford remote starter solenoid (a little over kill for the power requirements but they rarely fail and are very cheap)
The 10g wire mounts to one side and the small trigger wire mounts to the small center pole.
The other side of the solenoid goes up to the new plug that I also ran a 10g up to for the ground (rest of the wires are 14G) now have ignition cycled battery power to my 7 way plug in the bed.

The longest part of the job was looming up a 25' long harness

 

Thanks for the replies guys.
I have already run the 10g wire to the back plug and have the RV style solenoid mounted under the hood, just need to hook up the trigger wire.
I may have to look at figuring how to hook up a relay to a keyed power source like you did ratsun.

Thank you.