trailer brake service?

[dan newberry]

I recently purchased a 2015 GMS sierra 3500.  It has the trailer brake controller, but when I hook up a trailer that has electronic brakes, I get a service trailer brake.  After research I replaced the trailer brake switch.  I hooked up a trailer and upon initial hookup, everything seemed fine, then when I moved the brake controller to apply brakes, I heard a slight click and the service trailer brake came back on.  With the new one, the warning stays on with the trailer removed but the old one, at least it isn't coming on when the trailer is not hooked up.  Can anyone suggest or point me in the right direction as to wires/ or anything else to look at?  The trailer in question works fine on other trucks.