jd 650 won't start

On that starter if you can't get voltage at the starter wire from the switch trace it back checking the wire and at the switch. I don't think they have too much wiring on them as those were alot more simpler than the newer stuff. Does yours have an electric clutch for a belly mower ? if so these have an electronic interlock box that I had one go bad on our 750. I did replace it,but was able to bypass it same as if it was not equipped with a mower clutch option.

I really appreciate everyones input and help. I would really like to get this fixed back up so my 77 year old dad won't be jump starting it anymore!

The fix is to have a solenoid relay setup off of a John Deere 2520 tractor and wire it in so that the starter gets the full 12 volts at the solenoid.

I did this on a 950 which had the same problem as you. Although I can't remember how this setup worked, if you talk to a reputable john deere dealer and mechanic, he will tell you to wire this relay in.

This fix solved the problem.. and 5 years later, it is still starting right off.

The starting circuit is a black and white wire that goes from the starter to the key switch C terminal. It also goes through 3 saftey switches I mentioned before. You NEED continuity through these switches. NOT TO GROUND as you mentioned before.

To check the key switch for continuity when in the start position you should get continuity on posts B to BR, B to C

In the on position continuity B to BR posts. Hopefully they are marked at the switch.

And for future reference if you do ever have trouble with the front pto interlock you can test it by bypassing it by hooking the green and blue (kinda purple ? )wires together to get the clutch to work.