MT20D glow plug system?

[Rebeldad1]

I checked my glow plugs with a meter. Key on in glow plug position there is no voltage. The wire from the glow plugs to the relay is ok. The other larger wire to the relay gets 12V with key on. I now have two small wires. One gets battery power to the relay with the key in glow plug position. Where does the other go? How do I know the relay is bad? and where do I get a replacement relay?
Thanks

Also would like to get a wiring diagram for this tractor!!!