Finally solved this mystery thanks to Andrew Welburn (
http://www.andys-arcade.com/) and Hugo Holden (worldphaco.com).
As it turns out, the Pong PCB outputs composite video. Although the original game has a "television", it has been modified to bypass the demodulation circuits and serve as a monitor, not a TV. So the screws that look like UHF/VHF inputs are just used as terminals.
The single wire on VHF is the audio signal. The wires on UHF are composite video (signal and ground).
To get it to work with a modern television, the video wires from the game need to go to the composite video input (yellow RCA jack) on the television. The audio signal wire from the game goes to audio input RCA jack on the television. You will need to add a ground wire for the audio.
This game should now enjoy several more years of use.