My brake controller only slows down my trailer, tried several different ones, when slide the lever manually. Even set as high as it goes, it does not work with the brake pedal. It lights up the harder I push it, but no trailer reaction. What can I look for?
Thanks

 

What year truck?

 

2006 F350 crew cab short box 4wd Auto

 

Page 501 this forum has a good thread on this subject only for 05

 

Here' some good info:

It is assumed that the trailer brakes are operating correctly if the towing vehicle and trailer remains at rest with engine idling, automatic shifter in drive, and no application of vehicle service brakes.
However, the Ford TBC works differently from all currently available aftermarket trailer brake controllers because of its integration into the vehicle giving it the knowledge of the vehicle's behavior (speed, brake pressure, etc). This difference is why some inspection stations have been ticketing Ford vehicles. The Ford TBC has a manual activation device as do aftermarket controllers; but, it does not function in the exact same manner. At very low speeds, including at rest, the Ford controller sends a proportionally smaller amount of output voltage (though not zero) to the trailer brakes to provide smoother stops. This low-speed adjustment is the reason manual activation of the Ford TBC cannot be used to verify the operation of the trailer brakes.

The TBC output voltage also is adjusted according to the gain setting – for lower gain settings (which are assumed to be the case of a lightly loaded trailer) the output voltage can be very low and, for a gain setting of zero, the voltage will be zero.
The Ford TBC manual activator is to be used to calibrate the appropriate gain setting of the TBC. This gain setting determines the maximum available output to the electric brakes. Calibration is performed by driving at speeds between 15 and 25 mph (24 and 40 km) and manually activating the trailer brakes. If they lock up, the driver is to tune the gain setting down to the level just below wheel lockup. For a heavy trailer, the gain setting may be set high; for a lightly loaded trailer the gain setting may be low, but these also will depend upon road conditions. This is the primary and only suggested use by Ford for manual operation of the Trailer Brake Controller. In addition, the Ford TBC is capable of detecting and indicating certain faults in the tow vehicle wiring and the trailer wiring/brake system to the operator.
At zero speed, the trailer brakes are operable with the Ford TBC by activating the towing vehicle brakes and therefore satisfy all applicable brake operating regulations. The trailer brakes will be controlled and operating as designed, but not at the application level that can be expected from aftermarket TBCs due to the circumstances noted above. Since Ford has evolved the state-of-the-art in TBC technology, we recommend that inspection criteria evolve to accurately assess correct trailer brake operation regardless of which TBC is used.


The full document is located here:
CVSA : CVSA Programs : North American Standard Level VI Inspection Program
Bulletin number 2005-01

In other words if you're going fast enough you should be able to lock the trailer brakes with the manual lever but at slower speeds and lower settings it will just slow down as you described. Also in the article are some basic testing techniques and wiring diagrams that may be useful for you.