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Old 09-28-2017, 01:36 AM   #1
Tomakze
 
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Default Added OEM Tach, but it's not getting a signal.

Like the title says, I found a tachometer in a junk yard, and figured out how to modify my cluster to make it fit, but it doesn't work. I got one that plugs directly into the OEM harness, thinking it would be plug and play. When it didn't work, I checked the diagrams for the tach on AllData to figure out what each wire does. There are two black ground wires, 12v ignition, and the signal wire. I metered them all, and the only one not working is the signal wire. There should be some AC voltage on that wire with the engine running, but it is as dead as a door nail. What am I missing? Do I just need to hook that up to the blue tach wire under the hood that people use for aftermarket tachs? Or is there something simpler?

As a side note, I added intermittent wipers today as well. Best upgrade ever!
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Old 09-28-2017, 01:57 AM   #2
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Dont think you can test the signal with standard testing equipment. Maybe you got a dead tach.
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Old 09-28-2017, 02:15 AM   #3
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Naw, it is just AC voltage. A standard multimeter should pick it up easily.
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Old 09-28-2017, 03:12 AM   #4
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AC? Not pulsed DC? Depending on the pulse widths a digital meter will miss it. My cheapo digital meter will miss blinker signals. Got special ones at work to pick up clock signals and such. An analog meter has none of those issues.
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Old 09-28-2017, 06:04 AM   #5
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is the tach resistor present in the wire harness behind the driver headlight? there is a bundle of wires above the coil that are taped together. there are two plugs that should have something plugged in them. i posted a picture of the tach resistor a while back.
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Old 09-28-2017, 07:22 PM   #6
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Quote:
Originally Posted by Deerhurst View Post
AC? Not pulsed DC? Depending on the pulse widths a digital meter will miss it. My cheapo digital meter will miss blinker signals. Got special ones at work to pick up clock signals and such. An analog meter has none of those issues.
It should display AC volts on even a cheap meter... unless Nissan did something weird with the signal going to the gauge, which I find very unlikely. (for instance, many modern cars transmit tach information via data, but I can usually still find the tach signal under the hood) I install remote starts for a living, and they need a tach signal so they know when a car has started. You test the wire by looking for AC voltage that should fluctuate with engine speed. I've probably tested thousands of tachs this way.

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Originally Posted by cadillacdude1975 View Post
is the tach resistor present in the wire harness behind the driver headlight? there is a bundle of wires above the coil that are taped together. there are two plugs that should have something plugged in them. i posted a picture of the tach resistor a while back.
Now that is new info! What the heck is a tach resistor, anyway? I will have to look for it when I get home. If it isn't there, could that prevent the signal from reaching the gauge? Do we know the value of the resistor so I could test it?

And thanks, guys! I really want this stupid thing to work!
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Old 09-28-2017, 08:16 PM   #7
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all i can do is post a picture of the item. the following pics are off google, but it is the exact item your looking for in that taped up harness.







and here is my image and the post about this little pesky bastard.



http://www.infamousnissan.com/forum/...32&postcount=5
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Old 09-28-2017, 09:20 PM   #8
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That is insanely helpful! I bet that is my issue! In the 2nd photo you posted, the wires look like they corroded and broke off... what do you want to bet this has also happened to mine, and that is why I have no signal! Thank you! I will check this tonight!
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Old 09-29-2017, 01:54 AM   #9
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i fought an issue with my tach flopping around for three years. i changed the tach 3 or 4 times before i stumbled across a buried thread here on IN.
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Old 01-07-2018, 11:25 PM   #10
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Guys, without those resistor the tach doesn't work at all? When it is missing what can we do to replace it? How can we solve the issue?
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