Ford 3000 diesel - starter won't run from key switch

I can jump 12v directly to the solenoid and starter turns over great but when I use the key it will not activate - I have power to the solenoid connection when I turn the key either to start or to the thermostart position but it will not activate the starter ... no clicking or anything. I cleaned the connection on the 12v line from starter to the switch - I do have a new switch I am putting in tomorrow but am thinking that is not my problem. Anybody got any ideas?
Thanks

Neutral safety switchband?

Try that again. Neutral safety
switch bad?

Not sure which tranny you have, but our 5000 ever once in a while I have to jiggle the range shifter in neutral to get it to crank. So far it's maybe 4 times a year so I'm not digging into it yet.

Would I still have 12v at the solenoid connection on the starter when I turn the key to the start position if the neutral safety switch is bad?

Do the generator/alternator light and oil pressure light come on
when you have the key in the run position? I have a 73 4000SU
Gas that does nothing when key is turned on. Tried changing
solenoid and key switches. No improvement. Id be interested in
what you find.

My thoughts mirror John and Stevob.
Check your neutral safety switch.

Yes, you could. Think of it this way: If I have an old-style metal water pipe that is 99% rusted up inside, but still passes just enough
water to make a small stream, would that be enough to register on a pressure gauge? The answer is yes, and it would read full system
pressure, the same as the source. However, I don't have nearly enough volume to get any work done.

Same with your start circuit. The starter solenoid needs volume (amperage) to do what it needs to do. Pressure (voltage) alone won't do it.

(quoted from post at 05:08:12 07/18/21) Would I still have 12v at the solenoid connection on the starter when I turn the key to the start position if the neutral safety switch is bad?

Click to expand...

It depends on how bad the switch is, and how you measure the voltage. If you use a multimeter or a test lamp and measure the voltage between the end of the wire disconnected from the solenoid, and ground, you will get the voltage when the system has a very low load. Multimeters and test lamps draw a very low amount of current, you need a larger load to detect the problem in the system.

Connectors, wires, switches, relays and other components can have damages that will let through a small current, but not a larger current from a work load. That can lead to wrong conclusions when you measure continuity or voltage.

Connect a bulb for a car (~ 60 W) instead of the solenoid. It should not glow bright with key in start position. Now you can bypass the safety switch and turn the key to start position in a safe manner. Follow the two wires from the top cover for the transmission, there should be connectors under the shroud that you undo and connect the incoming wires together. If the bulb glows bright in start position, you have a problem with the safety switch or its harness.

If not, there is a problem somewhere else. Disconnect the wire that feeds the key switch, normally at the "B" lug on the voltage regulator and connect the end to a jumper wire that goes to battery (+). Try the key switch.

If nothing happens, move the jumper wire end to the lug on the key switch that connects to the solenoid (bulb). If the bulb glows, reconnect the safety switch and try again. If the bulb glows, the "downstream" wiring is OK.

Switch the jumper to the feed lug on the key switch and try with the key in start position. If the bulb glows, the key switch is OK.

When all tests are OK, reconnect the feed wire to the "B" lug at the voltage regulator, and try to start.


Please, do not leave the safety switch bypassed. Fix the problem instead.

I wasn't aware of a safety switch until now - saw a reference to it in the shop manual wiring diagram but could not find anything out about what it does. I don't think mine was working ... never had to make sure the high/low was in neutral - if that is how it is supposed to work, just turned the key and it would start?? Tried it earlier today buy wiggling the H/L range lever but it didn't make any difference - would not activate the starter. I am thinking I have a poor connection as was mentioned. Just curious ... since I have the earlier key switch with thermostart heat and start to the left and run and start to the right does it rule out the key switch as the problem since it does not activate the starter in either start position? I'd like to focus on the most likely cause first.
Thanks
And yes the idiot lights do come on in the run position.

You say you jump 12V to the solenoid...Which terminal re you jumping to that makes the engine turn over?
As primitive as all of these tractors are the one safety feature they had was a neutral safety switch. They didn't waste money on frivolous stuff, the NS is a there for good reason. I would make sure it was in the circuit.