Need to get a multi meter and follow the electricity down the lines until you find out where the disconnect is. I went though this last summer. I started at the fuse under the hood, then checked after the relay, there is nothing but wires between the relay and the plug for the clutch so then went to the plug on the ac clutch. I had power all the way but the clutch wasn't engaging. So I put 12v to the pins for the clutch and it did in fact engage. My problem turned out to be that the pins at that plug weren't making a good connection. I cleaned all those connections and I actually had to slightly bend the pins to make sure they were making a good connection. I haven't had any problems since.

 

 

The grey/white wire coming out of the relay goes right down to the clutch. There is nothing between the relay and the clutch on that grey/white wire. If you have power though that grey/white wire with the AC turned on then you should have power down to the clutch unless that wire has been severed somewhere between the relay and the clutch or a bad ground on the clutch. Here's the wiring.

 

 

Personally I would trace the grey/white wire and find out what is wrong with it but, yes you could run a new line for it. I don't recommend that but it is your truck.