To use this you just unplug the 8 pin plug in your jukebox and plug the above between the existing cable and socket.
Flip the switch one way and it's freeplay the other and it's normal operation.

It can be built like this or put into a box.

This adapter circuit should work for all  M100A, M100B, M100BL, M100C, HF100G, HF100W, HF100R, HF100J, and HF100JL.
Unlike a version that is being sold on ebay this circuit will not release a single button press.
In other words, if one key (letter or number) is pressed and a second is not, the latch solenoid will remain on and not release.
Though a big deal is made of this elsewhere, the engineers at Seeburg didn't think it was a problem in retail operation, since the same thing would happen if coins were used. Unless your a bit nuts you will turn the power off on your jukebox if left unattended for a long period of time or when not in use and keep an eye on it if small children are around it when it's on!

It works by supplying a ground to the selector leaf switches which latches the selector solenoid.  As long as the letter / number combo is completed the buttons will release and credit light will go off.

When time permits I will enhance this by adding a time out ct to disable the above if selection is not completed in a set time.
Which could be adjusted.

If anyone has the time and adds the timeout feature let me know, I'll include it here.

Here is a quick and easy method to add freeplay to Tormat Seeburg's

By adding a micro switch to the coin reject mechanism, credits can be added by pressing the reject button.

Parts Needed.
1- block of wood
1 - micro switch with long flat arm
1- length of wire (12")

Bend the end of the reject wire up so that in the button up position the switch is pulled up.
Connect the wires so that in this position the switch is open.
Pressing the coin reject button down will activate the switch.

The 2 wires are connected to the coin switch. (red and black for $.25) and to the micro switch.

Keep the coin mech open (not locked into closed position). Makes pushing the button a whole lot easier since you don't have to fight the spring on the coin mech.

Note: to put the jukebox back on coin, just pull a wire off the switch and close the coin mech , latching it into the bracket.

A switch could be added so that a wire wouldn't  need to be removed from the micro switch to disable the reject button credits.

One final thing, check the credit unit to insure that credits are being subtracted. If the unit was on "freeplay"                       (solenoid always on) then most likely 2 arms have been bent inside the credit unit. They will be bent away from the nylon gear . This is done to stop the credit unit from subtracting credits which allows for endless selections.

Thats it.
There is one potential problem with this method. If you use the button and reach max credits any additional credit may cause excessive current and blow the protection fuse in the credit unit if it has one. Exhausting credits before adding more will stop this problem.