Cannot get air supply to trailer

I just bought this truck, 2007 WS 4900, I flew out west picked it up and driver it back. Today I washed the truck and whenever I do that I always blow air through the gladhands to get the water out, so when I push the trailer supply I get nothing. First thing I thought of was the TPV so I pulled both likes offbefore the valve, push to supply air and still nothing. My next thought was the dash valve, now this truck has the 3rd blue tractor valve on it as well and when I pulled the dash down it looked like it was not from the factory this way (there are three separate valves, I believe factory has the tractor & trailer valve on the same valve block?) I've pulled the line off for the trailer delivery, push the valve in and all I get is a small puff of air and that's it. Is this valve my problem? I'm the third owner and the previous owner only had a fifth wheel wrecker on it, never pulled a trailer. Is there a chance that they have some lines mixed up when they added the other valve? Also when I have the trailer valve pushed in and pull the trolly brake it hisses air out the trailer service line.

 

Thanks JB7 I will see if I'm getting air to the trailer valve and go from there. I'm probably going to get a factory 2 valve setup and ditch the 3rd to clean up the mess they have under the dash. But of course all the lines are black so I wanted to make sure it was all plumbed correctly so I can mark the lines.