Electrical question, 7 prong trailer plug...

[Pont]

Ok, I wasn't really sure what section to post this question so I will ask here.

I just finished wiring my trailer plug on my truck and there is a place for an "auxilary power" lead on the 7 prong plug. I want to run a power lead from my truck back to my travel trailer to charge the trailer batteries while in transit. Instructions say to wire it to the fuse panel or a fused lead off the battery. Ok, so I wired it to a keyed accessory on the fuse panel but because of the batteries on the trailer having power, it feeds the power back to the fuse panel and powers my accessory without my turning the key on. Then I decided to wired it to the ignition switch to the cold side (only hot after I turn the key on). That worked great, until I tried to turn my truck off. It feeds power from my travel trailer back to my truck and keeps my truck running after I turn the ignition off and pull the keys out.

So, do I need to run this power lead through a toggle switch where I cut cut the power flow or do I need to install some sort of relay to stop the flow of power back to my truck from my trailer? Thanks for your help guys...........

Pont