Check for voltage on the battery cables at the starter- the one wire from the solenoid should go right to the starter. When cranking, it should be 10-12v on both ends of that wire. -if ivoltage is about 12v at the solenoid- the solenoid is working (both big plugs at the solenoid should be about 12v, and should be the same.)
-If voltage is about 12v at the starter when cranking, then the wire is good- your starter is bad.
-If voltage is not about 12v at the starter, but voltage is 12v at the solenoid- and you are sure you are working the same wire- then you have a broken or defective wire.