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 Coil Negative 
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Joined: August 11 2010, 11:34 AM
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Post Coil Negative
Hi,

I want to connect an aftermarket tacho on my 95 K8 V6 mx-3.

Now everyone says that u need to use the red wire closest to the front bumper on the 3pin plug.

However my wiring is differt.

from front bump to rear:

Blue
Red
Yellow/Blue

so i tried connecting it to the blue wire, Rpm stays @ 0

Tried hooking up to the other 2 wires and the gauge goes nuts. Not a steady signal but going from 500-3000 @ idle.

Switch on gauge is set @ 6 cil.

Any suggestions?


August 11 2010, 11:48 AM
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Post Re: Coil Negative
If you have a test light, just probe the thin-gauge wires at the distributor for one that flashes the test light rapidly. It's AC, that's why the test light flashes.

**Edit: It should be a yellow with blue stripe wire.**

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August 11 2010, 12:11 PM
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Post Re: Coil Negative
The yellow/blue should be te tacho signal yeah, but the manual says connect to coil negative which should be the red wire..

but either way all wires aint working. I cant get a solid rpm rate. The original tacho works fine (so i dont actually need it, but its fun with the shift light and digital numbers).

dont have a test light, but i do have a multi meter. does it matter wich kind of wire u use? I've used 1mm 12v wire.


August 11 2010, 1:10 PM
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Post Re: Coil Negative
Jforce wrote:
The yellow/blue should be te tacho signal yeah, but the manual says connect to coil negative which should be the red wire..

but either way all wires aint working. I cant get a solid rpm rate. The original tacho works fine (so i dont actually need it, but its fun with the shift light and digital numbers).

dont have a test light, but i do have a multi meter. does it matter wich kind of wire u use? I've used 1mm 12v wire.


Negative coil is usually considered tachometer signal.

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August 11 2010, 2:03 PM
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Post Re: Coil Negative
okay, maybe i can connect the wire behind the instrument cluster?


August 12 2010, 9:17 AM
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Post Re: Coil Negative
Jforce wrote:
okay, maybe i can connect the wire behind the instrument cluster?


One wire goes to the tach signal

One wire goes to ground

One wire to a switched 12 volt source (ignition)

Usually one wire to dash lights for illumination.

Shouldn't be difficult. You should have a testlight before attempting any wiring jobs, they're cheap enough. Never just go by the wire colors that others tell you.

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August 12 2010, 9:55 AM
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Post Re: Coil Negative
yeah i know it should not be difficult.

my tach has 3 wires

1 for 12v source
1 ground
1 signal

so i looked in the manual for the correct wire, wich should be on the 3pin plug.


I tried ALL 3 wires, but it is just not working.

1 of the 3 should work because 1 of the 3 IS the tacho signal.

I don't understand it should work but somehow the signal is screwed.


August 12 2010, 3:10 PM
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Post Re: Coil Negative
What did you connect the 12 volt and ground wires to?

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August 12 2010, 3:20 PM
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Post Re: Coil Negative
This is why we put a 1K ohm resistor in the tack input wire when doing the HEI mod. You have the right wire, but there is too much current getting to your tach. That's why its going crazy.

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August 12 2010, 4:22 PM
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Post Re: Coil Negative
12v is connected to a igniton on source.

ground to body just under the A-pillar.


so i have to buy an 1000 Ohm resistor and put this between the coil negative and the signal wire of the tach?


August 13 2010, 1:31 PM
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Post Re: Coil Negative
Jforce wrote:
12v is connected to a igniton on source.

ground to body just under the A-pillar.


so i have to buy an 1000 Ohm resistor and put this between the coil negative and the signal wire of the tach?


Yep, Wytbishop is right on there. I can't believe I never thought of that...

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August 13 2010, 2:03 PM
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Post Re: Coil Negative
hehe, okay il try this.

now i only have to find the correct wire, as my 3pin plug is colored different than other mx-3's.

see if i can find a test light.


August 13 2010, 2:29 PM
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Post Re: Coil Negative
Jforce wrote:
hehe, okay il try this.

now i only have to find the correct wire, as my 3pin plug is colored different than other mx-3's.

see if i can find a test light.


It should be the yellow with blue stripe wire on the 95 GS. If you set your multimeter to AC that wire should register a voltage.

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August 13 2010, 2:34 PM
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Post Re: Coil Negative
by the way, im not doing an HEI mod (yet), so the stock Ignition Coil has already an 1K ohm resistor build in. Right?


yes but that signal is interrupted. And the guys from my mx-3 club say it should be wire B on this diagram:

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which is the Red wire.


August 15 2010, 4:33 PM
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Post Re: Coil Negative
So in that diagram...the wire which is labeled "Tachometer" and shows a resistance in the circuit doesn't strike you as the correct wire?

The one labeled "C" in the 3 pin connector?

I'm just throwing it out there...I'm no expert.

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94' GS, black on black, now in several small pieces...and one large crushed piece.
2007 Mazda3 GT Sport --- super fun
2004 Honda RC51 --- Lost forever to some theavin' bastard
My Worklog
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Never attribute to malice that which can be adequately explained by stupidity.


August 15 2010, 11:56 PM
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