It is going to be tough to find a picture of the bottom of that amp, it is vintage.
If you look at the page that unreallstunner posted, on the schematic it shows a relay that was bolted to the back of the Amp where the hole is....if you look closely you can see the outline of the bottom of the relay on the inside of the case.
It must have had a bad relay and someone pulled it to replace it and never got around to finishing.
If the coil smoked in the relay, that would account for the toasted color of the wires in that area.
That is what all the un-hooked wires go to.
You need the proper relay, and then mount it and have someone that is familiar with working this stuff wire it up for you.
If you are not familiar with working on these old tube amps, you are going to need to get some help, there are lethal high voltages in that thing when it is plugged in...and some times even after they are unplugged.
It uses 110 volt on the coil of the relay, and switches 600 and 800 volts on the contacts.....these things can kill you.
73
Jeff