Help with MD 12 volt set-up

Fallon · Nov 8, 2009

Can anyone tell me the correct way to put a 12 volt battery set up on a Farmall 1948 MD. My MD has the 12volt battery on it now but the mag is not hooked up to ground out. To shut her off we always ran it out of fuel. Just had the mag rebuilt and I would like to know the correct set-up to run the 12 volt

CNKS · Nov 8, 2009

As you said the mag uses a grounding switch--it should have only one terminal. The battery voltage has nothing to do with the mag, it is not supposed to be connected to the mag. Sounds like you need a new switch. You simply run a wire from the stud/nut on the mag to the switch. If the mag was rebuilt, any internal problem with that connection should have been fixed.

Geoff NY · Nov 8, 2009

<MD"s have a switch on the front end of the manifold to ground the mag when you switch to diesel. If it"s not working properly pull the end cap and repair it (easy fix). Mine had the mag and had a second switch on the pedestal, which never really got used. Geoff

Geoff NY · Nov 8, 2009

My MD has a mag and it has a ground switch in the manifold that is activated when switching over to diesel. There is also one on the pedestal that I nver use. After cooling down on diesel, I switch to gas for a minute, then switch back to diesel and the mag is grounded, the gas is off and the diesel is off. If the manifold switch isn't working properly, take the cover off the front end of the manifold and you will see it's a quick fix.

D Slater · Nov 8, 2009

IH owners manuals for your model tractor said to switch to gasoline then shut gas off and let engine run out and die. Mag was only grounded from a short wire going to manifold switch. Some MD tractors had switches added like the gasoline tractors equiped with mags to ground mag. Some operators just shut them down on diesel. Lots of different opinions from operators on the best way to shut them down on gas or the diesel side.

Haas · Nov 8, 2009

The mag and the battery system are entirely separate. If original, the mag was grounded by a switch located in a chamber in the front of the manifold. The switch activated to ground the mag when in diesel mode. DO NOT connect any battery wire to the mag grounding terminal. If you do, the mag will need to go back to the shop again. If you don't want to use the switch in the manifold or it is gone or won't operate correctly, then install a separate switch to ground the mag. The mag should only be ungrounded when in gas mode. It's grounded in diesel mode so there is no spark at the plugs. To shut down the tractor, it is recommended to switch to gas mode, shut off the gas under the tank and let it run out of gas. After it shuts off, always pull the switch over lever back to diesel so that the decompression valves will be on their seats while they cool. Otherwise, the valves can warp and caus problems.

Roger46 · Nov 8, 2009

I guess I didn't realize that the distributer and mag MD's operated differently. On my MD with a distributer, there is an ignition switch on the column on the platform that the power to the distributer is wired through so you can shut off the engine in gasoline mode from the seat. There is still the manifold switch that shuts off the ignition when in diesel mode. I don't think I have ever shut off the engine in gasoline mode with the ignition switch, as I always shut off the gas and run it until the carb is empty or sometimes just shut it off in diesel mode. Roger

Help with MD 12 volt set-up

Fallon

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CNKS

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Geoff NY

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Geoff NY

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D Slater

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Haas

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Roger46

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