Tow harness connector not working

[pag04]

I tow a trailer that has a hydraulic surge brake controller. The controller has a solenoid to lock out the trailer brakes when I put the vehicle in reverse. The brake lockout is activated by the center pin on the factory towing harness socket. My problem is that there is no power to the center pin when the vehicle is in reverse, which causes the trailer brakes to engage in reverse. This is not a trailer wiring problem, it is with the vehicle socket.
Any ideas how I can debug this?
Thanks

 

[YelloLab]

Just had this problem. There is a small fuse block under the dash. It was a 10 amp fuse that was blown. There is a list of the fuses on the cover.

I know this because I replaced the solenoid on my trailer first because I didn't have blown fuses under the hood:redbrick: