Have a 32 kvm schwing 1990 on a mack frame....Was working and the boom stoped working?? went to manual and was  going to use the joy sticks and it still did not work, went under pump and switched hoses on bannana pumps and the boom started to work! changed filters ?? this also happened to the out riggers and the pump itself i switch the hoses and it starts to work strange !!!! Help!!!!!!!!!!!!!!!!!!!

  Check the suction hose from tank,the insides.

There is a solenoid on the side of the frame in a black box by the battery. This turns on and off the secondary mechanical pump. Try jumping with an alligator clip accross the solenoid. My 1990 would do this. 

Thank you we will check it out . Once agian thanks for your help !!

Also if its not that it could be an e- stop bad connection problem. This is easy to fix once you learn where to start and how to test each button. They are in series you have to start at the water box and test your way around the pump.