Couldn't resist responding to a mention of the "dinosaur" Hydraulic/electric controllers of the past. Actually the reason for their demise was the advent of ABS, which also varies hydraulic pressure.

They absolutely do not work with ABS. Controller manufacturers stopped the manufacture of hydraulic units to end any litigation from problems caused by their use with ABS.

In terms of function, they actually varied trailer braking in direct proportion to the pedal pressure applied to the tow vehicle. There was an initial point of shoe contact when the brake lights were activated, then the braking was modulated to the hydraulic pressure.

I've used them extensively, and prefer them to the all-electrical units, especially for their modulation. I miss mine.

Just thought I'd add to the information bank.

Good racing.

Bill