Have you followed those wires/hoses to see what they are connected to?

 

I have a Pac Brake in my 2003 RWD and you would have an air compressor mounted in front of the air horn. You would have power wires going there. There would also be a hose line and wiring going to the ECM area above the turbo area. You would have an on off switch mounted somewhere inside. Usually around the steering yoke area and going through the bulkhead by the parking brake. There is wiring going to the transmission on the left side as well. It took me a full day to do the wiring and mount the compressor. About a half day to mount the exhaust brake. Somewhere you would also have an accumulator tank. It is a fairly involved project, but I am so glad I did it with a 10K lb trailer pushing me down a steep grade.