I bought and installed a Redarc TowPro brake controller about 18 months ago, and it seemed to behave flawlessly until our current trip when the trailer brakes became very "grabby". I had to turn the controller down to 1 or 2 or the trailer would noticeably brake the car when trying to brake very gently. I called Redarc and they sent out a replacement controller which behaves very similarly, They are now telling me this is normal operation.
With the trailer hooked up in the driveway, I measured the braking voltage on the output of the Redarc Unit (Blue to White leads) while pressing the **** to test the system in both proportional and user-defined mode. This is what I measured:



The blue line represents the proportional mode and pressing the **** is supposed to mimic "light vehicle braking". As shown on the graph, "light vehicle braking" applies full battery voltage to the trailer brakes for any setting of 5 or above.
I don't see how this can be right. I would have expected the proportional mode to produce a lower voltage than the user-defined mode. Finally, if I set the controller **** to 5 or higher, I lock the trailer brakes with the lightest pressure on the brake pedal (i.e. no perceptible deceleration).
So... Questions to other Redarc users:

1. Do your trailer brakes come on aggressively on light braking to the extent that the trailer brakes lock up on higher **** settings?
2. What **** setting do you have your controller set to?

Further, if someone would make the same measurements as I did on a controller that seems to be working properly, I would be eternally grateful.

 

This is really interesting. I tow about a 5,800 lb Airstream. I've been using proportional control with a controller around 4or 4.5. I have be to fairly gentle with the brakes to avoid the trailer yanking me to a stop. I'll try to do the same voltage test you have in the next few days.