I have a 03 2500 HD D/A with a Sure Pull Pilot brake box with a digital display. When I pull my Fathers camper, a 20+ foot pull behind the brake box works a described. The display shows a "c" for proper connection and the numbers display higher as more power is applied to the trailer brakes. It also has a seven pin connection. My horse trailer has a smaller six pin connection which I use an adapter to connect to the truck. The problem I have is that the box doesn't show that the "c" for connection or display anything with the six pin. Seat of the pants feel is that the brakes on the horse trailer are working.My question is should the brake box work with a six pin connection or do I need to have the brakes on the hose trailer checked. Like I said it seems to be fine with a seven pin connection. Thanks in advance.
Also I forgot to say thanks to the ones who helped me locat the fuse for the trailer park lights.

The horse trailer is probably wired incorectly or if you are using an adapter it could be wired incorectly. Quite often on a 6 wire plug the brakes will be wired to the center pin but they should actually be wired to the pin marked A/S. I doubt you are activating the brakes on your horse trailer.

If you bought a Hoppy adapter it is wired the way Max Power said. You can get a Draw-tite 18160 and that sould fix your problem

You can also take apart the hoppy adapter and switch the 2 wires. There are only 2 wires that are reversible in it and they are the 2 you need to switch.

thanks guys I'll let ya know what I find out