2013 FREIGHTLINER CASCADIA TRAILER AUXILLIARY POWER?

I have no 12V power on the center pin at trailer plug, found no power at 30A 'trailer power' fuse and 'trailer power relay' missing at SAM chassis module. Install new relay, I now have power at the 30A fuse but still no power to the center pin. I have verified the trailer cord is good no wire break between the center pin and the other end of the wire where it plugs into the truck wiring harness. There is a break in the circuit from the SAM chassis module to the trailer cord connector, hopefully someone has done this before and can share their experience? I really need a wiring diagram for this circuit.

 

Can't do that, that's not fixing the problem. The trailer ABS draws power from this circuit, if you do that trailer ABS will be ON all the time running down the tractor batteries.

 

Well, today I crawl under the truck determined to fix this problem. I spread the wiring looms out and found the 'choke' that uncleal13 mentioned but it seems it has nothing to do with the auxiliary trailer power. I then found the trailer PDM (power distribution module) right on top of the choke, inside are all the fuses and relays for trailer lights and power. I found the 30A fuse for 'trailer ign power' blown, aha I thought this is my problem, replace the fuse still no power to trailer, I jumper the relay then got trailer power. I then tested the relay and relay coil power they are good, so somehow the relay does not turn on. Logically the SAM chassis controls the relay thus supplying power to trailer but how it does this I still don't know because I don't have the appropriate wiring diagram at hands.