Had to disconnect neg bat cable to stop starter fr

I hope someone can point me in the right direction. I have a 1955 850 that I converted to 12volt. All has been fine with the tractor. It starts anr runs fine, that is until the other day. It started with me having to pull on the starter button wire at the same time as I was pushing it to get it started. Now the tractor turns over constintly with out pushing the starter button or having the key in the on mode. I haD IT RUNNING FOR ABOUT 2MIN SO i COULD MOVE IT AND IT melted the two wires on the left side of the ammeter. Now the only way I can stop the starter motor from running is by disconnecting the neg bat cable.

I also jump started the tractor the other day and am wondering if that could have anything to do with this as it started after?

Thank you for any help you can give.

TK

Get a voltmeter or 12 test lamp and trace it back. Remove the cable from the starter and tape it up, Now you can trace back to the source of the problem without the starter cranking.

You'll find that the starter cable goes to a relay (commonly called a "solenoid", although it's not) under the hood. You will see the positive battery cable on one side and the starter cable on the other side. If you check the voltage on the starter cable, it will be 12 volts, which is wrong. You will also see one or two small terminals on the solenoid. Take the wire loose from one of these terminals and recheck the voltage on the starter cable. If the solenoid is bad, the starter cable will still be at 12 volts. If the solenoid is good, the starter voltage will drop to zero. This indicates a short circuit to ground somewhere between the solendoid and the starter switch. So you just have to trace the wiring back until you find the short. Note that the starter switch itself could be shorted.

Sorry if my instructions are a little vague, but since your tractor has been converted to 12 volts, it's difficult to say exactly how it's wired.

As far as the burned up ammeter wires, this is what normally happens when the starter gets "motorized". Once the motor is driving the starter instead of the other way around, it turns into a big generator, but with the wrong polarity. The high current flowing through the ammeter will burn out the ammeter wiring, or the meter itself, or both. You should just need to fix the wiring once your main problem is fixed.

Note that you could have both a bad solenoid and a shorted switch wire, since the solendid contacts might be welded as a result of the short. So if you replace the solenoid, just be sure and recheck the voltage to the starter cable before you hook it up.

One last note: You should be able to get a replacement solenoid at any auto parts store. Note that it's a 12 volt solenoid, since it would have been changed out during the conversion.

Melting the ammeter wires confuses me. The high current starting current is not supposed to be going thru it. The current NORMALLY required to energize the tractor ignition and starting ckt is less than 10 amperes. Wiring usually consists of 14 AWG at least (especially if it were 6 volts before) which is rated for 15 amperes constantly.

If you are still using your 6 volt starter, which most do, and converted to 12 volts, you are doubling the current to your starter thru the high current contacts of the starting solenoid. This could cause them to weld shut and cause the starter to lock up as you describe.

If you still have the 6 volt solenoid, you are putting twice the current thru the start switch and solenoid control winding, which may account for the melted wiring.

As mentioned, replace the wiring, the start switch, and get a new 12v solenoid being careful to get the right one. Then see what happens before you dig into the starter.

When I say the right one, I mean this. Your solenoid control wiring has to be suitable for your tractor"s hookup.

1. No transmission safety switch. The start switch supplies 12v to the start solenoid (via ignition switch being ON). Internally, the 3 TERMINAL solenoid has the low side of the control winding grounded (no 4th termanal).

2. Transmission safety switch. The Ign key is turned on supplying 12 volts to a 4 terminal solenoid (2 control winding, 2 high current). The 4th terminal goes to a switch on/near the transmission that connects this wire to ground when you push the button (if the transmission is in neutral) thus energizing the solenoid.

Chew on that for awhile and come back for more if needed.

Good luck

Mark