Ok all you electric guru's, I need some help.

I had a 2002 GMC P/U with factory 7 pin trailer plug, aftermarket brake controller, My electric trailer brakes worked fine. I bought a new 2013 GMC 2500 with integrated brake control, now electric brakes don't work, truck doesn't recognize brakes on trailer. All other lights/turn signals work.
I have read that sometimes the integrated brake control does not detect enough resistance from the trailer brakes.

My quesitons:
1) Anyone else have this problem with a newer GMC/CHEVY PU.
2) How do I test resistance on the trailer brakes?
2) How many ohms is enough resistance?
3) If there is not enough resistance, how do I fix it?
4)What else should I check?

Any help greatly appreciated.

 

When I hooked up mine, on a 04, cutting the factory wire that came with it, I was making it shorter , I blue the fuse.