The R7100, in standard form as sold in North America, could be powered from 12 volts DC or 120 volts AC. There is an internal power supply that converts the 120 volts AC to 12 volts DC to run the radio. The 12 volts DC goes in through the 4-pin Molex connector. If you want to use the internal power supply, you must have the jumper plug inserted into that 4-pin Molex. That's the plug with the red wire in the non-modified photo.
The internal power supply does generate a bit of heat. Using an external power supply keeps that heat out of the box. It looks like someone decided to remove the internal power supply, maybe because it failed, and add some other features. I like prcguy's idea that the selector switches are for CTCSS decode. I'm going to jump to the conclusion that the 5-pin DIN connector was for some sort of remote control feature that was added.
I agree that unless the seller can document the modifications, I would not buy that radio.