USDM AE86 TACH

jakes_hachiroku
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USDM AE86 TACH

Postby jakes_hachiroku » Sat Apr 06, 2019 11:35 am

so ik this is probably on the site somewhere but the search is kinda weird lol but this will prob be a quick one for you guys. so when i bought my usdm 86 3 years ago it just never had a working rpm gauge. finally got sick of looking at my aftermarket rpm gauge and decided to find what i think is the rpm wire (black with red rings?) and connect it to my ignition coil. still doesnt do a thing :( motor is a 16v 4age with weber dcoe carbs and msd ignition. would i be able to take said tacho wire and splice it into my msd ignition or am i missing something here? thanks! :shock:

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UNLIMITED 86
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Re: USDM AE86 TACH

Postby UNLIMITED 86 » Mon Apr 08, 2019 11:00 am

With the MSD ignition, you will probably need a tach adapter to get either tach to work.
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El Gato Felix
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Re: USDM AE86 TACH

Postby El Gato Felix » Tue Apr 09, 2019 6:03 pm

Yes you will need Msd's tach adapter Part Number is 8920 if you want to use the STOCK TACH. Otherwise your msd box should have a tach wire, BUT only works on AFTERMARKET tachs. This is what I bought when I installed MSD programmable ignition on my carbed 4A-GE. It's a little pricey, but if you want that stock tach to work you will need this plug in part.

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jondee86
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Re: USDM AE86 TACH

Postby jondee86 » Tue Apr 09, 2019 9:01 pm

Or perhaps one of these ?

Image

https://www.ebay.com/itm/TACH-TACHOMETE ... 2171581596

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jakes_hachiroku
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Re: USDM AE86 TACH

Postby jakes_hachiroku » Wed Apr 10, 2019 12:41 pm

Thanks guys! Always good help. I just hate my aftermarket rpm gauge and want to get my oem one working. So I'm assuming this msd adapter will work like the oem igniter would in terms of the rpm signal? Should be super simple to set up to my msd box

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jondee86
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Re: USDM AE86 TACH

Postby jondee86 » Wed Apr 10, 2019 2:26 pm

MSD puts out a 12V square wave tacho signal and you just need to convert that
to a "voltage spike" to drive an old school tacho. Most DIY converters use an old
relay coil and a transistor with some other bits and pieces set up like this...

Image

That is basically what will be inside the Ebay item. I don't know what is inside
the MSD part or how it works, but I guess they go a different route to get the
same result.

Cheers... jondee86
The reasonable man adapts himself to the world; the unreasonable one
persists in trying to adapt the world to himself. Therefore, all progress
depends on the unreasonable man.

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Re: USDM AE86 TACH

Postby UNLIMITED 86 » Fri Apr 12, 2019 1:41 am

It's likely similar in operation but my guess is that the MSD parts are potted into place to prevent failure from vibration (hence the box shape with flying leads).
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