Wiper Relays

Hello, I just bought this truck, and the wipers have stopped working. I am overseas military and took it to a mechanic, who replaced the wiper motor and then charged me $400.00 after he could not resolve the problem. I then took the truck to a local Ford dealer, who had to order the wiring diagram because this is a US model vehicle and not produced in the country I am stationed. Now, I am being told that it is the master relay and that these parts are very expensive. How can I be sure the Ford dealership is being honest with me? The parts manager said there are two types of relays. One is rather cheap, but the master relay is very expensive. If I were to get the code from the dealership, what numbers should I be looking for in order to tell me it is the master relay switch? Thank you!