MF135 starting issues and weird wiring

jleonardwv · Jun 22, 2019

This is my second tractor, so I'm still wet behind the ears. MF 135 Diesel 1966. I'm no mechanic but willing to learn.

It won't start unless I jump the solenoid with a screwdriver. That's caused by a bad solenoid or starter? Battery is fully charged.

Second, the wiring seems wonky. The key switch has ginormous wires running to and from. Same gauge as running from battery to solenoid. I thought the key switch was just to activate the solenoid/starter, not to run huge current through. Also the key switch barely works. I can hardly turn it even after spraying graphite in.

Third, the neutral safety switch is not in the circuit. I assume it was bad and therefore bypassed. Am I correct that the engine will theoretically start while in gear which would start motion immediately? If so, I don't want that. I want the neutral safety switch to work.

Fourth, I'm going to replace the ammeter (non-working) with a voltmeter.

I thought I'd try to fix all these issues at once.

Please advise.

1. I replace the starter/solenoid assembly? Any issues I should be aware of?
2. I replace the switch and run 16 gauge from the oil pressure switch to the key switch?
3. I replace the neutral safety switch. Any issues to be aware of? I run 16 gauge from the other post on the key switch to the new neutral safety switch then from there to the solenoid?
4. I run 10 gauge from the solenoid to the alternator?

Do I just eliminate the toggle start switch since my new key switch will now start the engine?

I'll worry about the voltmeter later, but I think I just wire it like it was a light without a switch?

Do I still kill it with the fuel shutoff thingy at lower left?

WranglerX · Jun 22, 2019

Solenoid may not just be activated by "Start" button or position on ign switch or defective... Need to test separately...

You sure "key" ign switch is not battery disconnect with a removable key .... Normally ignition switch has maybe 10-12 gauge wire from battery (maybe from solenoid terminal) to switch and then off to what ever need power....

Neutral safety switch disconnected mean yes it will start in gear... Safety issues here....

Yes a volt meter will be very informative as to electrical system condition over ammeter and a lot easier to wire....

Generally when you find a wiring harness bastardized or really butchered, it's usually easier cut it out and start over... you need to find wiring diagram of your tractor by make and model before tackling this job....

If it were me, I would run positive cable from battery directly to terminal on starter solenoid...

Get universal ignition switch, and you can wire it as ..

4-Position Ignition Switch

A 10 gauge wire from battery or terminal on starter solenoid to "BAT" terminal on switch.
A 14 gauge wire from "IGN" terminal on switch to energize fuel cutoff solenoid (if system has electric booster pump don't forget to power that) .
A 14 gauge wire from "ST" terminal to terminal on starter solenoid to energise starter solenoid.
Use a simple push button (or include relay if amperage a issue) to energise glow plugs... Be aware of possible need to have glow coil indicator in circuit or dropping resistor depending on glow plug voltages...
Voltmeter can connect one side to any circuit (IGN) the powers up when key "on" other side of voltmeter to ground..

You will have to deal with generator/alternator circuit, but you will probably have to get wiring diagram to work with that...

Safety switch may require just being wired between "IGN" terminal on switch and fuel cutoff solenoid to if you bail off seat (or not on board) switch goes "open" and kills power to fuel cutoff solenoid and shuts down tractor...

This is not a space shuttle, it really simple once you understand what it needs to run/stop...

Also be aware of my comments as I do a lot of automotive wiring but not diesel rigs so I am treating power (ignition on) to power fuel cutoff solenoid as if it were power to a ignition coil on gas engine....

Dale