My 2006 king ranch diesel dually has been progressively getting worse with both power drain/ parasitic draw on the batteries, it started first with the truck would start up on its own at anytime of the day or night, then with the alarm blaring, then the horn would blow at start up and not shut off, now when you hook the battery terminals up, the head lights, all marker lights come on, (even with the harness removed from the headlight switch) I have tried to trace it back by using a test light and removing fuses and relays as well as disconnecting any and all plugs from there respective components, nothing seems to work, i have replaced the dash cluster, disconnected all trailer light harnesses, both alternators, etc, whatever the smaller red wire feeds that is connected to the driver side +battery terminal is the culprit, any advise would be appreciated.
Thanks

 

There may be a problem with the security system. This will require a schematic wiring diagram, some measuring equip, and info exactly how the system is supposed to work.
Most places don't have access to the info or knowledge to troubleshoot a problem like this and because it gets a little complicated, your options are limited.

You can always inquire from a dealership what would be involved, and how much it it might cost to get it repaired.
They should have the info, tools and knowledge to fix it.