I'm pretty new to this bodystyle of Ford and I can't seem to figure out which plug is for the brake controller. I'm working on an 89 f350 dually. It has the OE trailer tow wiring. The harness and relay under the hood are there and the plugs are hanging in the back. What does the plug under the dash look like? Here is a pic of the only 3 unused plugs I have been able to find under the dash. Although, there are two plugs under the E-brake assy that are not used. A 2 pin with a constant 12v and a ground and an 8 pin. Thanks!

 

welcome to FTE. none of my pre 91 trucks came with brake controller plugs under the dash, i had to wire them for the controller.

 

C226, BLACK in color, 3 terminal plug.
Location is behind LH side of IP.