I was able to install a brake controller
that taps into the brake line. Unfortunately these are no longer made.
The units with a pedulum inside (nearly all of them now) are not worth a
**** for this application.

What? Oh dammit. I suppose someone did something exceedingly stupid and
then won a lawsuit.

Are the pendulum units attached to the truck body, trying to sense the
deceleration, or are they attached to the brake pedal, trying to sense
the rotation?

Its a decelleration sensor. If you are grossly overloaded going down a
steep grade. The damn controller won't help you stop at all.

The brake line pressure sensor is by far the best system but I'm sure
too many idiots f&*%ked it up when the took the line apart at the
master cylinder. A controller named Max Brake was made just for large
heavy trailers on small trucks. My truck is 22 years old, don't know
what to do when it dies.

My son's diesel F250 comes with an integral brake controller as part
of the car's system. Works better than the pendulum unit but stopping
distance was easily double of what my truck does with the same load.

Karl