MF203 Diesel Ignition Switch Wiring Help

fpappal · Dec 29, 2015

I am trying to wire in a new ignition switch purchased from MF. My old switch which did not work had four numbered posts. The #2 post was broken ff. The new switch has three posts on the back, however the first post has a smaller post attached to it. They are numbered 1,2,3, and the smaller post is not numbered. Does anyone know what these numbers relate to? I found an old post with a detailed wiring diagram, however that switch only had three posts and they were labeled S,H,and L.

The previous owner of this tractor bypassed the switch and added a push button to start it. Glow plug was never even hooked up. Any help would be appreciated.

DavidP, South Wales · Jan 3, 2016

Hi,
The wiring should be as follows;
Terminal 1 Supply from the starter solenoid via the ammeter, probably Brown
Terminal 2 Wire to thermostart starting aid (if Fitted) via a fuse probably Brown and Green.
Terminal 3 Wire to safety start switch and then on to energiser terminal on the starter solenoid. Probably white and blue from the key switch to the safety switch and then white and red to the solenoid.
I'm saying probably for the colours because US wiring looms may be a different colour to UK ones.

DavidP, South Wales

fpappal · Jan 3, 2016

Hello,
Thanks for the reply. Shouldn't one of these terminals go to the voltage regulator? I was trying to figure out each terminal last night with my voltmeter. The way I figured terminal 1 would go to the voltage regulator and the light switch. Terminal 2 would go the glow plug. Terminal 3 would go to the neutral safety switch. I was using this post as a reference. http://www.yesterdaystractors.com/cgi-bin/viewit.cgi?bd=mf&th=141417

The other issue I discovered is this aftermarket replacement is smaller than the hole in the dashboard. The only way it will work is if I weld in a new piece of metal and drill a smaller hole. I am going to call MF tomorrow and see if they have a different one. However this is the one they told me I needed.

DavidP, South Wales · Jan 3, 2016

Hello, this could be where the US and UK wiring varies. On UK tractors the brown wire from the live supply on the battery cable/solenoid terminal goes to one side of the ammeter. Brown and white goes from the other side of the ammeter to the 'A' terminal on the voltage regulator.
E earth
D dynamo
F field coils on dynamo
A Ammeter

Yes, early key switches did have a larger diameter threaded section. Most replacements now have a smaller diameter. Welding a disc and drilling it is the ideal answer but don't forget to drill the hole smaller so that you can file it out and leave the 'flat' in the correct place relative to the position of the switch. Originally they would have only had 'Off', clockwise 'Start', anticlockwise 1 'Heat', anticlockwise 2 'Heat Start'.

DavidP

fpappal · Jan 3, 2016

Thank you for the reply. Looks like I will be welding a piece of metal in there. Thanks for the reminder to drill it smaller. I am anxious to hear this tractor run but that won't happen until I get this wiring all figured out.

DavidP, South Wales · Jan 4, 2016

Hi,
It is not essential to have the complete wiring loom in place to be able to start the tractor. Does it have a pipe to the oil pressure gauge or an electrical connection? All you need to have is the battery connected. using a piece of substantial wire bridge the live battery connection at the starter to the solenoid connection which activates the starter. As long as you have a fan belt fitted there should be no problem in starting it and running until it is warm to be able to listen and observe how it is running.

DavidP

fpappal · Jan 4, 2016

Did you restore a 203? My goal this winter was to do a mechanical restoration. I didn't realize just how big the project would become. Wiring the dash is really the last thing I have to do. Good idea about starting it without the dash on. From what I have read this engine is tough to start after a rebuild because of air in the system. I am waiting on MF right now for a lower washer that goes the primary fuel filter. It is a paper cartridge style and the element sits on a rubber o-ring. The o-ring is held in place by a special washer that holds it, which is missing on my tractor. They tell me that part is obsolete so they are ordering me the one that goes with the oil filter(which is also missing on my tractor) to see if they may be similar. I am going to wait to start it until I get these in place.

DavidP, South Wales · Jan 4, 2016

Hi, I have not restored a 203 but have done many UK MF 35s with the same A3-152 engine in my 40-plus years of MF experience. If necessary you can always hang a clean 1/2 gallon or so can with diesel in it, onto the exhaust pipe. All you need is a small bore pipe to fit the inlet pipe to the lift pump and a return line back to your can. You can either start the syphon from the can yourself or vent the fuel system using the lift pump.

DavidP

MF203 Diesel Ignition Switch Wiring Help

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