2012 ram 2500 heavy duty

I am not familiar with Ram charge setup, but some others, you need to add a fuse under the hood to activate the charge line.

You should be able to check at the 7-pin connect, to see if a charge/battery line has power. My Ford, the truck needs to be running, for battery wire to be live.

If your camper battery is low, it will take quite a while, for the truck to charge it.

Jerry

The RAM should have constant battery voltage at the charge pin all the time and it comes with the fuses installed.
I would check the manual for a fuse number and location. Hopefully it isn't going through the TIPM. If it is, I would wire around it.

If it does not have the towing package on the Ram you will have to add the 40 amp fuse. It will be in a black fuse box in the engine compartment and will be clearly marked.

how do i know if it has the tow package?it has the integrated trailer brake and tow mirrors,but i don't know if they are standard equipment.

If you have the integrated controller and towing mirrors you have the towing package. Check the 40 amp fuse in the engine compartment to see if it's blowen. The inside of the lid on the fuse box will tell you which one is the trailer fuse. If its ok you will have to test the charging wire on the 7 pin connecter then at the batterys if that is ok.