JLG 40H voltage drop when switched to platform

Hey guys first time to this site. A wealth of information. I have a 1999 jlg 40h. When I switch it to platform control the voltage drops to 11v from 13.5 and about 20 seconds later the machine shuts off. My guess is something is shorting on the platform side, getting hot, and opening a solenoid. Or something along those lines. I haven't worked on a machine like this before. Any help would be greatly appreciated.
Thanks Josh

JLG 40H voltage drop when switched to platform