1. Loose ground will NOT cause a fuse to blow.
2. Monaco products(Roadmaster) the Air dump is indeed SLOW, that is a design function
3. I never paid attention to, if the system had more than 1 solenoid for manual dumping. I always heard the solenoid up front and did not know if there was one in the rear. What you need to do, since you found the front Air Solenoid is to verify it has 12 volts and ground when someone pushes the dash switch. If it DOES have 12 volts and ground then the solenoid is bad.
4. You can also get the system to dump by extending the Powergear Jacks. When the coach raises up the ride Height arms will move and dump the air until you can get the system fixed. Doug