Mars is very protective of their copyrighted manuals. You won't find any online. You *have* to buy the service manuals and interfacing manuals from them through an authorized Mars distributor. Mars service manuals are very expensive. I needed one for a particular model and they charged me $100. Mars bill acceptors also require some specialized test jigs/service tools/power cords that only Mars makes. When you talk Mars you're talking get out the wallet----ouch!
You will probably have to phone Mars directly to tell them what you need, then get all the part numbers and order thru a distributor.