MF50 Diesel - Starter Solenoid or Switch Problem????

Bill VA

Well-known Member
Bush hogged with the MF50 diesel yeaterday, it ran like a new machine.

Cold and damp here today, went to start the tractor, got a few turns out of the starter (good charge yeaterday) but the battery was weak and couldn't turn anymore. Not a problem. Got the jump starter, when I hooked it up, the starter tried to turn. It seems the starter solenoid never disengaged. So I quickly took off the jump starter fearing I've got a dead short somewhere between the switch and the starter solenoid. Power wire from the battery to the starter solenoid felt warm. I'm thinking, were it not for a weak/dead battery, I'd have melted wires or worse.

Before I tear into it - what do you think? Bad switch? Bad starter solenoid? Starter and solenoid are less than a year old. I'm kind of leaning to switch.

Any ideas? Anyone experience something like this?
 
Probably the solenoid, I've seen the contact washer stick to the contact bolts, especially with a weak battery. Used to hit the solenoid with a wrench when I heard it still engaged so it would stop on one tractor I had. A good rap would jar it loose..
 
Don't know that tractor well but if the solenoid has to the bigger studs on it as in one for the battery cable and the other to the starter use a heavy piece of wire and jump across those 2 big studs and see what happens. Of course make 1000% sure it is out of gear. If it spins over and starts that way then the solenoid is bad. If it does not turn over good then the start it self is going bad. Over the years I have gotten a good laugh many times when I start a machine doing that and my friends cannot start it no matter what they do
 
Disconnect your control circuit from the starter and test circuit with a multi-meter through a number of cycles and see if voltage always returns to zero. Make sure the insulation is good on the harness and not making a connection from one of the other always hot wires running with it. These one(s) should connect to the same terminal on the starter as the POS cable from the battery. They feed the ignition sw, ammeter, Lights,etc. If that's all good then test the starter using a remote start switch from the POS battery connection to the control terminal. Block your wheels if your standing next to it.
 
Put an ohm meter on the switch a few minutes ago and it's showing continuity in run and start positions. This would explain the starter trying to turn the engine continuously regardless of switch position. These 2 poles have red and black wires running to them, which makes sense. Essentially what I've got between these two poles is a spring loaded via key, momentary switch - energized and non-energized. Just like a push button switch and the only difference is the key (to keep someone from driving off with the tractor) is the push button.

There is a third pole that goes to the lights. I don't think this enters into the start circuit?

So I'm thinking the switch is bad, i.e. shorted closed and not returning to open after the key is let go/returns to the home position.

Question - if I were to unwire wire the switch - taking it out of the circuit and jump the solenoid on the starter itself, am I going to fry anything while I find a replacement keyed switch or rig a push button start switch.

Fuel cut-off stops the engine.

Thanks,
Bill
 
Here is a pic of the backside of the switch. Except for this instance, it's work for me like a champ since I bought the tractor - probably 17ish or so years ago.
a248580.jpg
 
Sorry I have been offline dealing with Ice storms. As long as you insulate your hot wire from battery to the switch It will not be a problem. Biggest risk is starting it while your not in the seat.
 
Thanks!

The other thing I think about is with a push button, anyone can drive off with the tractor, but than again, keys for these tractors are common as are screw drivers to jump the starter solenoid!

Thanks again,
Bill
 

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