If you have a on board air system there is no fittings that you can fill, man. you have to use the air system. I have a 86 Aspencade and went through the same ordeal, I had to take my system apart and get it working. Good luck getting it to work. MCFF
I am certainly not an expert on this system but as I recall the bike has to be in the accesory key position or some such for the pump to work. If it works out of the bike then the pump must be good. If you run 12 volts directly to it does it run in the bike. Possibly a bad ground? Just guessing and bumping you up.