My friends received a free soda vending machine manufactured by Dixie-Narco for their workshop (if you’re picturing a soda machine right now, it’s probably manufactured by Dixie-Narco). They wanted it put into free mode so they didn’t have to constantly pump quarters into it. I searched the the internet and found many many people adding momentary push buttons to simulate a coin deposit. I also found $50 one-off relays and even people selling $30 jones plugs to do it. I then found one post describing the right way to do it (cache):
Instead of jumpering pins and adding a button to the jones plug you can just swap a couple wires in the clear-cased vending relay and be done. No additional parts needed and no need to push extra buttons to get your soda.
First, unplug your machine. Following the illustration in the post you use a paper clip to eject wire 71 from the socket and tape it so it doesn’t short. You then eject wire 10 and insert it into the slot that wire 71 was in. Plug the relay in and it will now immediately vend soda when you push your selection.
I’m reposting this in hopes that people will find it and start converting their machines the easy way. The original poster says this is the manufacturer recommended way for converting to free vend.