The on/off Pressure Switch on this model is reference# 49 in the .pdf diagram which I've attached to this reply.
It should be threaded right on top of the #48 Manifold, which installs into the tank inlet. The motor cord and power cord should be wired into this Pressure Switch.
Yours may be missing (?)...can you upload a photo of your compressor?
Actually the compressor in the photos you uploaded looks just like the FL-3505 in the diagram I sent in my first reply; the pump is the same as well as the tank size and motor...the only difference is that your motor and pump are reversed from the unit in the diagram.
It may not look like it as sometimes it's hard to tell being it's a B&W drawing, but that's your compressor. The only difference that I can tell is that your pressure switch assy it located at the tank beside the electric motor, whereas the unit in the diagram has the pressure switch located beside the pump; otherwise, your compressor should be identical.
The on/off switch should be a lever protruding from the pressure switch body (unless it's missing), which you can see in the photo I've attached with the arrow pointing to it.
