Look on the section between the pump and the reservoir. That is where the release valve is located. There is a solenoid valve there that should have a light gauge wire going to it that energizes the it. The pump does not run when lowering the top. The solenoid simply releases the fluid from the cylinder to go back into the reservoir.
Do you have a manual for the Hi-Lo? That would help because it should give instructions to raise and lower and also electrical diagrams.
here is a link to the a 1969 manual which would be the same:
http://www.hilotrailerforum.com/f49/...on-voyage-836/
It appears from comparing the your photos and the manual's photos there have been some alterations made to the pump assembly.