Welcome to the Site. If you have the capability of sending a picture that may help others chime in with what you may need or let us see exactly what it looks like. If you are talking about the "vend relay" which plugs into the "jones" plug. I just bought one on fee-bay for $25.00. Brand new they are a little expensive.
The vend relay opens the circuit allowing power to the control panel buttons after the money is put in. I used to have square top Dixie Narco and had similar issue until I replaced the vend relay. I had coins dropping directly down on the coin mechanism ( Mars 6800-H). After the money is put it you can watch or here the vend relay open.
http://www.ebay.com/itm/Vend-relay-for-single-price-Dixie-Narco-soda-machines-/370538751264?pt=BI_Vending&hash=item5645d4a520Besides the vend relay I also had to replace the top half of the coin mechanism because the magnet was broken.
You may also check with Rod or Janet at Funtronics (
www.fun-tronics.llc.org)
Again Welcome to the Site and Thank you for your service!!
Hope that helps...
Jared