Regarding the solenoid: is it 12V or 24V? If powered from the PCM, there is a little jumper in the middle for selecting the output type. And how do you have the solenoid wired up?
Regarding fittings, any team of reasonable age in your area should have quite a few.
Regarding setup, what we have is approximately this, with everything in the top row connected by brass fittings (relief, guage, and switch all being on T-fittings).
Code:
compressor--relief valve--T fitting--gauge--switch--release
|
tanks--regulator--valves
And what MrForbes said.