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I have this same question in another thread, but it is way down the posting. The tach has four terminals on the back. The schematic is hard to follow, but appears that the upper left is a fused +12v wire which I assume powers the hour meter. The lower left and lower middle appear to be for the sensor but I don’t know if the wires can be interchanged. And on mine it looks like the middle terminal has 2 different wires attached. The lower right terminal looks like it gets a feed from the tail light switch, so I assume that powers the lamp. What I don’t see is a ground wire?
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I think your best bet is to contact a dealer and see if they can help you out. They work on these everyday or close anyway. The only suggestion I have is to take a ohm meter and ground one lead and with the other lead search for a zero or very close ohm reading and then trace it back to confirm that it is a real ground source. There is a possibility that the base of whatever you are looking at is grounded thru the chassis and all that is in the dash is the hot side , not requiring a ground there. But there will be a ground for the dash lights maybe you can figure it out from there. good luck
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A picture of the back of your tach would be extremely helpful.
Your reluctor consists of a coil of wire around an iron core. Nothing magic inside at all. All it does is measure the difference in the magnetic flux field as a flywheel tooth passes by, and this difference is seen as a sine wave. The reluctor has two leads, it doesn’t matter which one is grounded. If the reluctor has one lead, then the body is grounded
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Both are good points and pretty much what I figured. I am not sure why some of my pics load and others don’t as they all come from my phone. The gauges are separate & not in a unit assembly. And they are all installed in the fiberglass body so they are not body grounded. There has to be a ground connection at some point. Also, the needle is not on zero and affordable said the tach needs power to reset it to zero but that does not tell me where the power comes from or goes to. Common sense would dictate the hour meter power source, but again you still need a ground for a complete circuit. The sensor is 2 wires which would give a voltage across the wires and the one side could be grounded.
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You are correct. The bottom right terminal post (K) is for the light.
The center post (G) is for all ground connections. This must also be grounded to the engine/chassis.
The left post (S) is for one of the leads from the reluctor, the other connects to the ground. These two wires are probably siamezed in a sheath. There should only be one lead connected to the (S) post.
The red lead is the 12v+ feed from the fuse block and it also powers all the other gauges. It is fed from the key switch.
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That’s where I stand on it. Hopefully I can look into next weekend. I swapped out the switch, and I changed the wiring to add in a relay for the glow plugs and bypassed the faulty clutch switch, so I will have to trace wires again. I got my Chinese photo tach for a comparison when I get the tractor tach going.
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