Have a 2008 F350 that came with the tow package but not the trailer brake controller module. Bought one on ebay, installed a new master cylinder with the pressure sensor and had the dealer activate the unit. I have a message that says Trailer Brake Module Fault and the dealer says the gain seems to be set a 9.5 and won't adjust. They suggested putting in a new controller might fix the issue. So rather than wait for them to order a new OEM one at stupid money, I took the OEM one out and installed a new Reese controller and have the same problem, when it's adjusted to 0.0, the trailer brakes are fully activated when i touch the truck brakes. The slide on the controller gives me some flexibility to control the trailer brakes independently but still when I touch the truck brakes they go on hard. Bought another OEM controller from a wrecker and same thing happens. The truck was previously used as a fire safety vehicle on an air force base and they had lights wired in and a cap on it with a third brake light. I'm wondering if something could have been cross wired when they dismounted all these things and the controller is getting voltage from the lights somewhere. The failure of the reese controller to modulate the brakes strikes me as the key to a wiring fault. Going to start looking now but am wondering if anyone else has experienced anything like this and if they found a solution. Hoping to hit the road tomorrow with a functioning brake controller. Thanks for any assistance.