6G Celicas Forums

So I need to know which wire on the back of the gauges is for the tach signal. In digging around in google I have found that it should be either black, green, gray, or white with a blue stripe. None of those wires exist on the gauge wires except for the green which leads to a bulb. I know the black wire is on the tach, but I've already rewired my whole engine to get the Autronic SM4 computer set up, so no more stock igniter. Anyone have any ideas?

Is the car originally a 5S?

yes, originally a 5s

Directly behind the tach gauge are three screws that hold the tach in AND connect the plastic circuitboard wires to the gauge. Screws are ig-, ig+ and e. The letter "e" is behind each gauge. The e's on the gas gauge, speedo, and tach are all connected together. Is this "earth"? IG+ on all of the gauges are connected together, as well as a few bulbs, so this seems like it's the positive wire. That leaves IG-, BUT there are also others. B16 is labeled by the center connector, and connects to the two turn signals and also to the little black connector that unclips from behind the tach. (the connector has transistors inside, and maybe a small chip). A13 also comes out of this little connector and it by itself. The last wire is not labeled and goes through a diode prior to going into the connector.

This post has been edited by match220: Oct 23, 2012 - 3:02 AM

I believe its the gray wire at the tach. Here's the two diagrams, first one is the wires at the tach (note the gray one goes to the igniter module) and the second one is a power diagram which includes the wires going out of the ignition module. The IG- is the gray one.

http://bgbonline.celicatech.com/6g/electri...t%20cluster.gif

http://bgbonline.celicatech.com/6g/electri...%202.2l%201.gif

Press and hold CTRL key and + to zoom in.

I'm not at the car right now, but there are about 10 gray wires that go into the gauges. I'll look into these links though.

There should be only one going to the tach. If you have a voltmeter, check for continuity between the tach gray wire and the gray wire at the igniter module. That's your tach signal. Good luck!

it would be easy if I still had the black wire from the igniter. I pulled out all of the wires coming from the sensors to run the new harness for the Autronic. So everything is out. It's not as bad as it sounds, everything is wired in except the dumb tach wire. I couldn't think because I had old 5s wires everywhere, autronic wires everywhere, and new power wires for other things, so I had to rip everything out for clarity. There are old videos of the birds nest on youtube. I'll be making another youtube video probably at the end of the week if you want to see how it's coming along.

dude! That wire diagram is exactly what i've been looking for!!! It says the tach wire from the coil is A10! A10 is IG- on the back of the gauges. IG- is the signal! yay!!!

Glad I could be of help. Would be nice if you could report back later on progress.

Can't you pull a tach signal off the the 12v plug hot wire? I know I've seen some guy do it in his Mustang for a stupid cheepo tach w/ shifty light thing. He also ran on 7 cylinders >.>

So you're talking about the 12v positive wire from the igniter? I suppose it is possible since there is electromagnetic interference from the coil running through the wiring on the car. Every time I flip through AM radio stations on my truck I hear the interference. It wouldn't surprise me if someone figured out how to use the interference. My Autronic ECU is designed to run off of a tach signal though. And since I found the tach wire with the help of Syaroan I'll just run it off of the tach wire.

This post has been edited by match220: Oct 23, 2012 - 5:45 PM

The tach signal is a clean signal, with little to no noise and there is a dedicated wire for that purpose. It could be possible to pull a similar signal from another wire, but it might not be as clean a signal as the one going through the wire you've already chosen.

You know you're doing it right when it's not easy, is all I always say.

I had to take the tach signal for my Megasquirt from the distributor plug, because my igniter was bad. It's a tad noisy but it works. ECU came with a shielded wire which helps a lot too.

This post has been edited by Syaoran: Oct 26, 2012 - 9:24 AM