520 problem

I have a 1957 JD 520 which was running fine. Now when I start it, it starts but when I leave my foot off the starter it stops. As long as I leave my foot on the starter peddle (starter NOT engaged) it runs. I take my foot off the starter peddle, it stops. Can anyone tell me what is wrong? The starter has never been rebuilt. Could that be the problem? Thanks so much.

You most likely have a bad ballast resistor. The other possibilities are a bad ignition switch or a broken or corroded wire in the ignition circuit. Take a test light and ground one end and probe the battery side of the coil with the other end. With the switch on keep probing upstream until you find power.

"<font color="#6699ff">[b:654c4848f0][i:654c4848f0]As long as I leave my foot on the starter peddle (starter NOT engaged) it runs. I take my foot off the starter peddle, it stops.[/i:654c4848f0][/b:654c4848f0]</font>"

Take a look at the diagram below.



Note the black wire that is connected to the starter switch and ignition resistor.

Take a look at the photos below.



Note the side terminal on the starter switch.



Note the black wire connected to the side terminal on the starter switch leading to the ignition resistor.



Note the black wire from the starter switch connected to the "output" terminal on the ignition resistor.

When you press down on the starter pedal, power goes directly from the battery to the ignition resistor and coil at start up.

Take a look at the diagram below.





Once you release the starter pedal, the power comes from the ignition switch to the ignition resistor and coil.

"<font color="#6699ff">[b:654c4848f0][i:654c4848f0]Can anyone tell me what is wrong?[/i:654c4848f0][/b:654c4848f0]</font>"

You might consider using a test light to "troubleshoot" the ignition resistor first.

Take a look at the photos below.



Turn the ignition switch [b:654c4848f0]ON[/b:654c4848f0] and check for power at the ignition resistor "input" terminal.

If there is power, then check for power at the ignition resistor "output" terminal.



If there is power, the ignition resistor is good; otherwise the ignition resistor is bad.

If there is no power at the "input" terminal on the ignition resistor, then check the ignition switch next.

Take a look at the photos below.





Turn the ignition switch [b:654c4848f0]ON[/b:654c4848f0] and check for power at the [b:654c4848f0]IGN[/b:654c4848f0] terminal.

If there is power at the [b:654c4848f0]IGN[/b:654c4848f0] terminal, then the ignition switch is good.

If there is no power at the [b:654c4848f0]IGN[/b:654c4848f0] terminal, then check for power at the [b:654c4848f0]BAT[/b:654c4848f0] terminal.



If there is power at the [b:654c4848f0]BAT[/b:654c4848f0] terminal AND no power at the [b:654c4848f0]IGN[/b:654c4848f0] terminal, then the ignition switch is bad.

If there is no power at the [b:654c4848f0]BAT[/b:654c4848f0] terminal, then check the wire and connection to the battery.

Hope this helps.

James your illustrations and narration are better than any other troubleshooting guide I have seen.

Thanks for the compliment.

James Howell, FANTASTIC job! I admire your skill level. What part of the world do you live in?

Ditto on your illustrated trouble shooting guide. You make it easy James.

Excellent description James.

I had a 620 do the exact same thing. I replaced the starter switch, cleaned up all the connections and everything was fine.

One more thing I suggest is checking the points. When I was dealing with the 620, a retired JD mechanic said a lot of times it can be the points creating a lot of resistance. So when it goes from 12v to 6v after the pedal is released, it shuts off.

Thanks for the compliment.

We live on my granddaddy's farm in NE Texas - Morris County.

Thanks.

Thank you.