The wallbox can select one of 200 songs to play on the Jukebox. Each selection is a combination of one of 20 letters + a number 0 - 9 (20 X10 = 200 selections). When both a letter and number have been pushed a rotor rotates around a disk with contacts to generate alternating current pulses to represent the letter and number selected. For example, the selection 'B5' would send two pulses for the letter B and 5 for the number 5. Each pulse is a 24v alternating current signal approximately 42ms long, 3 - 4 60hz cycles. There is a 70 - 72ms gap between each set of ac cycles. The letters are sent first, followed by a 220ms gap, then the numbers.

The wallbox with the cover removed. I added the switch connected to the green wires under the contact wheel to bypass the credit reset solenoid - after the first coin is deposited the wallbox stays on freeplay indefinitely. I am sure there are other (better) ways to do this, but I could not find any documentation so I came up with this solution from studying the schematics.

Initially the signal from the wallbox was erratic - the pulses varied in duration and some did not happen at all. I cleaned the contacts (with contact cleaner) made a big improvement. You have to be carefull to not remove the silver plating from the brass contacts. The official Seeburg manual is very specific on this point. It also has instructions for setting the position of the rotor arm and the proper tension on the contacts. After cleaning and adjusting the pulses from the wallbox were consistently 42 ms long, +- 1 ms.