Tachometer Signal?

[Scotty]

The IV finally idles like its supposed to and I'm in the process of taking apart and revising the temp gauge. I will be going through the thermostat housing just because and a few other things, but the question of the day:

I went through my nice stack of receipts for things that have been or were done with my IV over the years (I do keep track but I don't care to do the math) and come across one from before I got Pita that lists work on its Jaeger Tach.

As it stands mine doesn't work but the light does, so it's grounded. How does the Tach wire into the car and where does the 'wiring' signal come from exactly?

It has the loops that are supposed to be on the back and there's no corrosion on the bar that brackets it to the dash. I had some issues where someone got into the car and fudged with the wiring which is why I had to rewire/redo my turn signal as well as my brake lights, so I'm wondering if I'm missing wires that should be on the Coil or somewhere else?

The main reason for asking is that I want to track the wires from their source back to the back of the device to make sure one isn't cut or been removed from where it should be.

Thanks gang!


EDIT: I found the section as to how it's wired. I'd still like to learn more about these and the differences between one that's been converted from + to - Earth and such.

 

[hierogk]

Check this link for a description of how they work.

https://circuitglobe.com/electrical-tachometer.html

 

[Bill Blue]

Check this link for a description of how they work.

https://circuitglobe.com/electrical-tachometer.html

I find that to be totally unhelpful in this situation. Does not even mention automotive electronic tachs.
Bill

 

[husky drvr]

Scotty,

If you've not found this article, then it will probably answer some of your questions. It will at least give you more info for more questions.

http://sunbeamalpine.org/wp-content/uploads/2017/10/alpine_tach_repair_rev5.pdf

 

[Tom H]

See my article for some understanding of these tachs

http://sunbeamalpine.org/wp-content/uploads/2017/10/alpine_tach_repair_rev5.pdf

But a few simple points:

1) if the car has been converted from Pos to Neg earth then the tach would need to be converted as well
2) you say the loop is present on the rear, but if the tach was converted from Pos to Neg earth then the loop would need to be reversed
3) The tips of the steel C-Clip that holds the loop in place must make good contact with the mating tips peaking out from inside the case
4) in addition to the loop on the rear there needs to be a separate wire to the spade lug to power the tach
5 If the wires are different than original, (eg, white wire looping thru the rear and also a white wire powering the tach), it's a good possibility that the wiring is not correct. Many aftermarket wiring kits do not wire the tach correctly,

Tom

 

[Tim R]

To add to the above replies, I have found that the 'loop' of wire on the back must be the correct way round as per the picture in the manual. If it is looping the other way round it simply won't work.

Tim R

 

[Tom H]

To add to the above replies, I have found that the 'loop' of wire on the back must be the correct way round as per the picture in the manual. If it is looping the other way round it simply won't work.

Tim,

You gotta match the picture you use to the polarity of the car's electrical system. The correct way the loop goes depends on whether the car (and Tach) are Pos or Neg earth.

 

[hierogk]

I find that to be totally unhelpful in this situation. Does not even mention automotive electronic tachs.
Bill

It was meant to show that the direction and speed of the pulses from the coil through the wire loop on the tachometer induce the movement of the shaft the tachometer needle rests upon. With faster engine speeds, the coil fires faster and the needle on the tachometer moves farther around the face of the instrument.