Tractor Repair: New Holland TC29, safety interlock switches, starter solenoid

Question
All of the safety interlock switches are working properly, the battery is good, yet, when I try to start the tractor it just clicks 1 time. It's like something is still not making the connection. Could it possibly be the starter or starter solenoid? If I take the starter off the tractor, is there a way to test the starter &/or solenoid to see if it is working properly without purchasing a new starter & solenoid? Thanks for any advise, David

Answer
  First check all the fuses.  Then check that the battery is good and that the connections are clean and tight.  Turn the lights on and see if they work OK or if they are dim.  See what happens to the lights when you try to start it.  If the lights go out, you have a bad connection somewhere. Check the battery ground cable where it grounds to the chassis and make sure this connection is clean and tight and does not have paint or rust between the cable terminal and the tractor.  It should be bare metal.  Check the connections on the starter, sometimes these are loose or have overheated and arced.  You can verify if the starter is good by taking it off as you said, and hooking jumper cables to it from a known good battery.  Short the battery cable terminal and the ignition switch wire terminal together and the starter should turn.  This is the safest method.  Or you can do this with the starter still on the tractor, but only do it with somone sitting in the seat holding down the clutch pedal to prevent it from running you over if it should start and move unexpectedly.  Once the battery, connections, and starter are verified to be good and if it still doesn't start, then there is still a problem in the safety interlock system.  Besides the switches, there could still be a problem in the wiring or diodes.