Truck batteries discharge

[pinetar]

That would be easy to do mine is black wire though goes to positive. There is no negative wire on my trailer to pwr jack.

[richinny]

i've seen dome lights come on when a vehicle is put on a lift. it could be the added weight is causing a light (under hood light, door, glove box, or courtesy light is coming on.

[TG Twinkie]

The frame of your coach is the negative side of the circuit for the tongue jack.
I agree that the problem is in the TV. If you have access to any type of trailer that has a similar or greater tongue weight. Perhaps you can duplicate the problem and eliminate your coach.

[Tom Nugler]

Looks like we can rule out the trailer as a source of the current draw.
I pulled up the AllData wiring diagrams and specs for the truck in your profile. With a dual diesel battery system without an isolation relay, if the batteries are fully charged and in good condition it would take a huge draw to drag them down to the point where the engine wouldn't start in a short amount of time.
Take the truck into a good shop and have them do a proper charging and starting system test. I'd start with a battery capacity check with the batteries disconnected. According to AllData they are wired in parallel. The counter boy at AutoZone or Pep Boys won't have a clue as to how properly to set the handheld they use to check batteries.
After that the usual alternator output check, cable resistance and condition, and starter draw and connections.
You've got to start with the basics.

Good Luck,
Tom

[twobikes]

We once had a GMC that discharged like that (only in far distant places after towing). We traced it to a short in the wire linking the two batteries. Dealer installed the second battery by routing cable behind radiator, enough miles and the chaffing resulted in the mysterious intermittent discharge ( and lots of heartburn)

[Matthew014]

Way too many cooks in the kitchen. PM me if you have any questions I can help you with.