While up under my dash I found a trailer brake plugged in on my 97 F350 that I picked up a few months ago. If I unplug the trailer brake then the engine wont start and when I plug it in then it starts right up. Where was this connector originally plugged in before the after market trailer brake was installed? I dont have a trailer and would like to pull out the trailer brake but dont know where the original plug is...

 

There is nothing that it plugs into. It shouldn't be shutting off either just from unplugging the controller. It sounds like the last owner wired it wrong somewhere.
If it says UHAUL anywhere on it then that is the problem right there! Bunch of idiots!

 

it isnt wired in, its plugged into a factory gray plug, just not sure what that plug is for?

 

No one knows?

 

try and post a picture of it

 

The plug is a factory plug , it shouldn't have any effect on starting. Look inder the dash & see if someone may have tapped into any of the wires...

 

Yep like Rick said that gray plug is the factory provision for the controller.

 

So that pigtail has to be wired in, im guessing that if I trace it back and pull it out then everything should work ok