The hydraulic line model like you describe has a very small cylinder and it has a pin that pushes a metal strip across a resistor. IF it pushes it all the way down due to high enough hydraulic pressure then you have full brake current. There is a preload spring adjustment to regulate the hudraulic pressure needed to get full braking on trailer.
When ABS was introduced on trucks these were discontinued and the reason widely touted was use of these with ABS would instantly condemn you to HELL. I used them for years on ABS equipped trucks and purposely braked to get ABS active and observed no ill effects. I got electronic units and scrapped them and went back with the hydraulic type until an electronic style with a pressure sensor that mimics this old style was introduced.
Keep using it until leaks. It even works with electric over hydraulic trailer brakes, something many electronic controllers, even factory fitted, can't claim.
When ABS was introduced on trucks these were discontinued and the reason widely touted was use of these with ABS would instantly condemn you to HELL. I used them for years on ABS equipped trucks and purposely braked to get ABS active and observed no ill effects. I got electronic units and scrapped them and went back with the hydraulic type until an electronic style with a pressure sensor that mimics this old style was introduced.
Keep using it until leaks. It even works with electric over hydraulic trailer brakes, something many electronic controllers, even factory fitted, can't claim.