Help Tracing Electrical Starting Problems - JD2020

mn212 · Aug 23, 2016

Hello,

I'm trying to chase down starting problems on a 60's JD400 Industrial tractor. This model is very similar to a JD 2020 utility. It has a 4 cylinder gas engine rated at ~ 60 HP. It will crank fine but doesn't seem to have spark to start while cranking.

In my trouble shooting, I ran a test lead from battery positive terminal to coil positive terminal to try to eliminate any wiring issues.

Here I what I observed.

I turn the key to start. It cranks and starts with the test lead connected. But while the test lead is connected the engine cannot be shut off with key. The engine remains running when test lead is disconnected. The engine will not shut down until test lead is disconnected AND the key turned off. Does that make sense?

I would have thought if the wiring were bad the engine would stop when test lead was disconnected. It seems like a relay somewhere is latched in by the test lead connection and the relay will not drop out until the ignition key is turned off

Suspected problem components - starter solenoid, ignition switch, or bad wiring somewhere.

How would you trace this problem down?

Zebrafive · Aug 23, 2016

There should be two wires on the coil + positive post.
One runs to the starter solenoid to give the coil 12 volts for starting (hotter spark). I think this wire failed. So your test wire replaced it. But your test wire does not "drop" out when the IGM switch goes from "start" to "run"

The second wire is a resistance wire to lower the volts to coil when the IGN is in "run" this is to extend the life of the points. I do not think this wire is "powered" when the IGN is in "start" only "run"

So your test wire, got it started. then the resistance wire keeps it running. Which you confirmed by removing the test wire and it kept running.

The starter solenoid should have four wires. Large post two wires, one from battery and one to alternator. Then two more terminals with smaller gauge wires. One is to the IGN to engage the starter, this one may be labeled "S". The other is to the coil + positive terminal, this one may be labeled "R".

I would run a test wire from the coil + to the starter solenoid, "R" if labeled. I am not sure of the wire color, it might be light blue.

If all works as it should, this the wire to replace.