I doubt if there is another fuse. You might look for a solenoid close to the hydraulic pump or mounted directly on it.
First thing would be to see if any voltage is getting to that solenoid when you try and lower the jacks. If no voltage then you'll have to start back tracking from there.
If there is voltage you might try tapping on the solenoid. If that doesn't work then try replacing the solenoid. If that doesn't do it then the only thing left is the pump.
Do you have the wiring diagram for the jacks?
Air forums # 1674
1974 20' Argosy Motor Home
1975 24' Argosy Motor Home
1974 31' Excella trailer (parting out, as of 4/1/2015 I have wheels & windows left to sell)