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Tachometer Wiring

Scotty

Silver Level Sponsor
I know there are a lot of posts on this subject, which I have gone through. I want to make sure that I'm not somehow being an idiot and that this 'new' Tach I picked up wasn't a potato.

Here's a pic of how I have it wired:

49D600D3-9E99-4704-9088-9CDBFFF19684.jpeg

If you look at this will the hole for the light bulb at the top, the white wire on the right is going to Coil +, the white wire on the left is going to power to the ignition switch and the green wire is going to 12V being drawn from the fusebox. Multimeter shows it's getting power. I also used a pair of 'wired' Alligator clips and clipped one side to the light hole and the other to the ground screw that would normally ground the Control Box just to make sure the housing was grounded.

I expected it to work and it does nothing at any RPM.

Do I have it wired right or is it a potato? This is a later Negative Ground Jaeger Tachometer 2416/00 RVI.

Please educate me. Thanks fam!
 
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spmdr

Diamond Level Sponsor
things to check:

-Good ground, does the light work, when installed?

-Proper Dist Dwell, point gap.

-proper Coil and ballast resistor, may cause too low current through Tach white wire

try adding more loops under metal U clip, without the plastic.

-proper metal U clip seating over white wire loop.

-proper polarity of the white wire loop, not usually a problem unless wiring changes.

change the loop direction, in a different location of the wire than the plastic.

DW
 
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hartmandm

Moderator
Diamond Level Sponsor
I think you got the loop direction correct and also have the wire to the coil on the inside of the loop.

Mike
 

Scotty

Silver Level Sponsor
Negative ground tachometer. Positive ground S-IV. Hmmm?
My IV is converted to negative ground. I do run a Hitachi Alt after all :)

Is there something unique with the IV’s wiring that could be something I’m missing? I’ve been using an aftermarket Tach from Autozone and it’s having no problems working.

I’ve considered swapping out and updating the gauges so they all match but led displays is where my inner purist draws the line. Plus I like the Jaeger look.
 

Scotty

Silver Level Sponsor
Scotty,

Do you have a Pertronix ignition installed?

Might be relevant, but probably not.
I do have electronic points. Not made by Pertronix tho. They’re the type you swap the points and condenser for. The unit I have is specifically made for the Lucas Distributor we use.
 
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spmdr

Diamond Level Sponsor
If you change Ignition components away from stock, Tach function gets a bit sketchy.

The Tach seems to have a narrow tight list of requirements to work properly.

...and the old tachs seem to get more finicky as they age.

DW
 

Tom H

Platinum Level Sponsor
Key question- is the white wire that lops through the rear of the tach the ONLY wire providing power to the coil? If there is a additional wire powering the coil then the tach will not work. The loop on the rear is how the tach senses the pulses of current going to the coil. If there are 2 paths for power, then the tach is only sensing about half the energy or less. How about a photo of the wires going to the coil and dist. As it's a series IV, I assume it has no ballast resistor near the coil.

Also you changed polarity of the car. If this is the original wiring harness, then the loop on the rear is backwards after changing car polarity. I will read again your description of which end is wired to which part to verify if it's right or wrong now. Mike already addressed the issue but I' don't know if he understood that was a Neg earth tach now installed in a converted polarity car.

Tom
 

Tom H

Platinum Level Sponsor
From your description, "with the lamp hole at the top" etc, your loop is in the correct direction. I am puzzled as to how you achieved that when you changed the car's polarity. Did you cut the white wire before and after the loop and then swap the ends? Original SIV wiring would be backwards for a Neg earth tach.

Edit, BTW, this tach is from an Alpine GT fastback.

Tom
 
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Scotty

Silver Level Sponsor
Scotty, did you resolve your tach issue?

Tom
I did! Thanks for your help!

Sorry I’m so late in answering your question. Also, my SIV’s white wire for the Tach was cut and had spades put on when I got the car. The Tach I picked up had the same arrangement on the back.
 
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