I have a 94 6.5 I use for towing a 25ft 5th wheel . A friend has a d/max with his 5th If the batterys in his 5th get low he just plugs in the trailer plug and it seems to run off the truck batterys .It has the factory plug set up .With mine it won,t power it off the truck unless I use jumper to the trailer batterys . Any one know what I would have to do to make it like his.