1st the GM controller works great!!! but it is to sensitive and you need to install two electric brake magnets on the truck or trailer frame and hook them into the circut all the time, Just put one on each side of the frame and put a bolt through them and wire them in.
This will give it more LOAD and will work fine.
2nd You need to open the fuse box under the hood and make sure the large wire is hooked up and fuse installed, there is also one for the battery charge line.
If you follow this you will be very happy with the new unit, for further info log into "thedieselplace.com" and you can read all about it