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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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

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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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.

UNLIMITED 86
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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).
IG: unltd_86

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jakes_hachiroku
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Re: USDM AE86 TACH

Postby jakes_hachiroku » Wed May 15, 2019 11:34 am

Ok guys! so ive finally had the time to install the msd tach adapter annnnnnnnnnnd………… NOTHING lol so now im lost lol is there another wire for the usdm tach that looks similar to the tacho whire?

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jondee86
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Re: USDM AE86 TACH

Postby jondee86 » Wed May 15, 2019 11:44 pm

On the USDM GTS the tacho gets its signal from the black wire on the igniter.
The SR5 will get a signal direct from the coil negative. The black wire finds its
way to the big square(ish) plug on the firewall behind the engine, and from
there to the OEM tacho.

According to this diagram...

Image

... all you need to do is connect the black wire (that leads to the tacho) to the
violet wire out of the tach adapter. Note that the tach adapter needs its own
key-switched 12V supply and chassis ground.

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.

jakes_hachiroku
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Re: USDM AE86 TACH

Postby jakes_hachiroku » Thu May 16, 2019 4:37 am

Yes I wired everything just like the picture with the black wire to the violet on the adapter. but did I grab the wrong wire? I used the wire that is black with what looks like brown dots on it? is this not right?







jondee86 wrote:On the USDM GTS the tacho gets its signal from the black wire on the igniter.
The SR5 will get a signal direct from the coil negative. The black wire finds its
way to the big square(ish) plug on the firewall behind the engine, and from
there to the OEM tacho.

According to this diagram...

Image

... all you need to do is connect the black wire (that leads to the tacho) to the
violet wire out of the tach adapter. Note that the tach adapter needs its own
key-switched 12V supply and chassis ground.

Cheers... jondee86

aukword1
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Re: USDM AE86 TACH

Postby aukword1 » Thu May 16, 2019 7:41 am

Sounds like the right wire, you might have to trace it back and see if there are any shorts on it. Even possibly that it could be the wrong wire there are a few that look the same.

Image

jakes_hachiroku
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Re: USDM AE86 TACH

Postby jakes_hachiroku » Thu May 16, 2019 7:54 am

IT does look like the idle up and rpm gauge wire look similar so I will look again it just sucks cuz the previous owner cut a lot of those wires haha


aukword1 wrote:Sounds like the right wire, you might have to trace it back and see if there are any shorts on it. Even possibly that it could be the wrong wire there are a few that look the same.

Image

UNLIMITED 86
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Re: USDM AE86 TACH

Postby UNLIMITED 86 » Fri May 17, 2019 1:23 pm

Hopefully you have a multimeter.

Set it to check for continuity and test between the "black" wire you think is for the Tach, and the black wire going to the igniter.
IG: unltd_86

Parts for Sale: https://offerup.co/profile/ae86

WTB: OEM Windshield, hatchback 3rd brake light, and a clean Kouki Trueno Front bumper (also willing to trade mine + cash/???)

jakes_hachiroku
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Re: USDM AE86 TACH

Postby jakes_hachiroku » Wed May 22, 2019 8:41 am

ok so i have double checked that it is definitely the correct wire that i used for my tach adapter so now im not sure why it wouldnt work unless the tach is actually bad lol the one thing i havent tried doing is simply putting the tach directly to the msd box without the tach adapter :?: so until i can figure this out i guess my autometer tach is going back in :( thanks for the help and pics guys you always help me out ;)

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