IH 656 electrical

Pilot199 · Jun 27, 2018

The lights on my '69 model 656 diesel suddenly went out recently. I went through the wiring under the control panel & fixed a couple of nicked wires. I've got 12 VDC through the fuse block but not at the rotary light switch. Fuse is good.

When I put a jumper wire to the light switch, the lights worked but the jumper wire got firey hot quickly, so I've got a short. I tried tracing the hot wire but it disappears into the wiring harness. I inspected every wire I could see & can't find a short or even find a wire that's arcing.

My manual doesn't have much of a schematic, just drawings. Has anyone run into anything like this?

Thanks,

Gary

caterpillar guy · Jun 27, 2018

Look for places in the fenders or any other place where the wires go around sharp and not so sharp locations. After 45 years they get wear through the insulation. In the grill if the lights are in there as they go by the heat shield by the fuel tank and such.
Put a meter on your switch could even be there.

Duner Wi · Jun 27, 2018

I know the 766 had a bunch of wires that ran thru the fire wall behind the engine and ahead of the fuel tank. There was no grommet in the hole and wire wore thru and shorted.

used red MN · Jun 27, 2018

How heavy was the jumper wire? Some of those el-cheapo jumpers are not very heavy. If you are using a 16ga wire and it gets hot you probably do have a short.

old · Jun 27, 2018

If you have a VOM take the power side wire off of the lights and then check for a ground on the power wire. If you find low ohms then you know the wire is shorted some place. If you have high ohms then one of the lights could be bad and have a internal short

Lpakiz Larry · Jun 28, 2018

I discovered a procedure about 30 years ago that helps find a problem like this.
Remove the fuse and replace it with a headlight sealed beam bulb, and connect each side of the bulb to the fuse terminals. The idea is to use the filament as a fuse. When there is a load thru the filament, the bulb will glow anywhere from bright (dead short circuit to ground) to just barely orange, which would indicate not much current flowing thru it.
Now go and wiggle wires, disconnect individual components, whatever and wherever you suspect a problem.
If the intensity of glowing light bulb changes, you are very close to the source of the problem.

A variation of this is to use a very small dash light bulb to check for very small ?leaks? by unhooking one of the battery cables and hooking the dash light bulb in series. Bulb should not even glow when everything is shut off. If it does, you have a leak or draw, and can eliminate possible causes by pulling fuses one at a time, unhooking components, etc.until the bulb goes out.

Pilot199 · Jun 28, 2018

Just to be clear, I'm not getting any power TO the light switch. I loose the trail somewhere after the fuse block.

The jumper I used is 16ga. so I must have a pretty direct short.

I can't figure out why I'm not seeing a spark or smelling a burning wire somewhere.

Y'all have given me some good suggestions to search this thing out. Unfortunately the tractor is at my place out of state so I'll have to wait a week or two.

Thanks for the info. gentlemen. I'll try to let you know what I find.

Gary

cuby · Jun 29, 2018

Un hook ground cable from bat. place a test light in between grd. on bat and grd. cable. If light lights there is a short. Move wires around until light goes out. Neat little trick that I was told on this site. Eliminates a lot of guess work.

IH 656 electrical

Pilot199

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caterpillar guy

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Duner Wi

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used red MN

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old

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Lpakiz Larry

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Pilot199

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cuby

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