Advice needed on electrical M4900

[bbirder]

Hi Guys,
Need some help figuring out my problem. Something not working in my starting circuit. Solenoid will not engage with the key. I have changed both start relay and key switch with no luck. I have jumped the neutral switch and disconnected the PTO switch and still nothing. I start my tractor by jumping the solenoid to the hot on the starter. I have a schematic of the wiring but I'm stumped on this one. Any ideas where I can check next?

M4900SU

 

[Soundguy]

I'm not sure how kubota runs it.. but onmy larger fords.. I check power at the start terminal on the key with a test lamp.. then check it thru the NSS, then, thru any other interlocks.. etc. somewhere power is dropping out.

On some NH's.. they swap a relay into the circuit and let the relay power the starter solenoid.. IE.. the key switch circuit with all the interlock switches inline only powers a relay, which in turn powers the start solenoid.

Follow the volts... somewhere you are dropping it and not completing the circuit.

soundguy

 

[rbargeron]

I'm not sure whether the M4900 has one, but from your description it sounds like maybe the fusible link. It's a short loop of heavy red wire with a white plug - usually located near the starter. I've had two of these fail - the wire corrodes inside the connector to the point it doesn't conduct enough amps to bring in the solenoid. If it is completely rotted off, then there would be no lights on the dash either. The solenoid takes almost as much current as the starter itself - so the wiring and connections have to be good. A corroded fusible link can be deceptive - because it will test ok for voltage, but when it has to conduct a lot of amps, it won't. You can check it by unplugging it and substituting a short piece of solid copper #14 or #12 house wire. A new fusible link is under $10 - most dealers keep a couple in stock. Hope this helps. As always, prompt cheerful refund if info is bogus. Dick B

 

[bbirder]

Thanks for the feedback. I realize that I'm not getting a complete circuit. Although the keyswitch is difficult to get to on this model, I might have to tear into it to trace my voltage. Thanks for the tip on the fusible link ! I hadn't thought of that. It will be next Sunday before I can get into it again, but I appreciate the input.

 

[Soundguy]

The solenoid takes almost as much current as the starter itself - . Dick B

You've got to be kidding.

if so it's one of the worst designs in history!

soundguy

 

[Soundguy]

If there is a fuseable link inline in the solenoid circuit.. trace / diagnose it just like a piece of wire..

follow the volts.

soundguy

 

[rbargeron]

You've got to be kidding.

if so it's one of the worst designs in history!

soundguy

It's not that unusual for the solenoid to draw 15-20 amps. My Chevrolet's did. The starter takes another 20-30. It's not a bad design - the inrush of a motor is steeper than a solenoid.