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Field resistor Partnumber

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Rexalot

07-31-2007 12:28:57

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Anybody know what the partnumber is for the field resistor that is on the back of the light switch on a Farmall H?

Would this be a dealer only part or are there any other sources? Still available?

Thanks.

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Janicholson

07-31-2007 19:00:13

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Re: Field resistor Partnumber in reply to Rexalot, 07-31-2007 12:28:57

Rex, there are two resistors on the old LHDB light switch. One is for the lights, ant it is only used for dim lights it is located between two terminals, one of which connects to the lights. When the switch is turned to D, the light power goes through the resistor (a replacement would be a 3 or 4 ohm power resistor (ceramic wire wound) with about 80 watts of capacity. This can be soldered into the connections with short # 12 high temp wire (from appliance repair) By the way, the lights should work without the resistor on B.
The L and H positions are for a three brush generator with a cutout relay only on the side of the gen. This depended on the operator to adjust the charging rate during the day to prevent overcharging (turning to L from H) A resistor is also used in that circuit, for the L position to ground the field through the resistor to ground. This is totally separate from the light switch connections. The same type 3 or 4 ohm resistor can be used for this, (could be 50 watt, but does not matter) wired in the same way. Use of a good ohm meter to make sure which connection is which is a good idea.
I would use a later model real voltage regulator to make it better, see Bob M's diagrams. JimN

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Rexalot

07-31-2007 12:55:38

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Re: Field resistor Partnumber in reply to Rexalot, 07-31-2007 12:28:57

My '49 H still has 6 volt system. Is there another way to wire that will let me use this switch to operate the lights and charge the battery?

This is a new aquisition for me. Tractor hasn't shown any charge on the ammeter and none of the lights have worked (bulbs looked ok, haven't checked with meter). I opened the box up and the obvious is the resistor is melted away.
I've gone ahead and replaced all the wiring, just down to this resistor.

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ScottyHOMEy

07-31-2007 16:42:53

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Re: Field resistor Partnumber in reply to Rexalot, 07-31-2007 12:55:38

I got lucky on mine and found that the failure on the field resistor coil was only because the end of the windings had lost contact with the copper pop rivets that provided the screw connections. A little flux, a touch of solder and it works. though it did make some prety impressive smoke when it mad esome hat for the first time in many years!

Is the strip still there? Can you rewind it.

Lights aren't working either? What kind of shape is that resistor in? If it looks okasy, you might want, just for kicks, to take the back off the switch and check the contacts inside. There's a spring in there, but it's big, and the layout is pretty simple, both mechanically and for the puzzlin' out.

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Rexalot

08-01-2007 03:13:38

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Re: Field resistor Partnumber in reply to ScottyHOMEy, 07-31-2007 16:42:53

Resistor bar is completely melted away. Nothing left. I do have a new voltage regulator to put on. I'll try doing just that first if all the resistor is for is "dim" lights. I think I can do without those.

I did check with my local IH dealer. Resistor by itself isn't available. I would have to buy a whole switch at $43.00

I'll be looking for a used switch someplace for later or I may just make my own using your suggestions of what I need ohm/watt wise. I already have Bob M's diagram.

Thanks

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