2006 with trailer hitch wiring issues

[nondem]

I bought this truck new in 2005 - one of the first 10,000 sold. It's got 75K miles on it now.
I had the OEM Honda receiver hitch installed by the dealer before I took delivery.
I've used it quite a bit with various trailers.
For those not familiar - the OEM hitch has two separate connectors: One for lights and trailer brakes(round) and another for just lights(flat).

Problem: The brake and turn signals don't work on the trailer. I'm using the flat connector. I've got 3 trailers with working lights and they all do the same. The tail lights do work but the brake/turn function doesn't do anything.
All the lights on the actual truck work fine.

I visually inspected the wiring and it all looks fine - undisturbed with no outward sign of a problem. The lights all worked fine less than a week ago and all of the sudden this.
Where should I look? I could easily buy a $20 light kit and install it but the OEM stuff looks better and I expect to need the trailer brake function soon.


FYI: The only problems I've had since I got this truck were a bad plug connection on the heat/ac blower fan and the Security light holder on the drivers door is partially caving in. Besides regular maintenance I've done brakes all-around and am currently needing new tires.
One note on the brakes - the rears wore out before the fronts!!!!

[Ridgekid]

The trailer feeds don't come from the lights, they are fed from the controller under the dash. That has relays and is fused. The first thing to do is check your fuses. I suspect one is blown or one of the relays is gone. By the way, when you test, use a lamp/voltmeter or trailer connector tested and no the trailer. It is poosible that a short in the trailer blew a fuse.