Tacho output on 99 MS2
 

Is this circuit ok as tacho output? 12V ok? 1K resistor ok?

http://www.msextra.com/ms2extra/Gene.../LowVTacho.GIF

Where do I wire it to on the tacho? The factory wiring manual isn't very clear about this as speed and tacho come from a processor inside the cluster. Am I supposed to I hook it up directly to the tacho itself?
I found several older threads that talk about the tacho, but nowhere could I find where exactly to wire it to.

I completely forgot about the tacho when 'designing' the circuits on the proto area. I'll have to get creative to find a useable spot on the board :squint:.

I there a way to make a tacho output without having to free up an output? Everything is used already so I'll have to give up the output for WI or EBC :ugh:.

That's the circuit I used, works perfectly. From looking at the wiring diagrams, it does indeed look like you're going to have to cut directly into the processor.

Though wait a second, if the taco is driven by a processor on the cluster shouldn't it just work anyway? If not it looks to drive more than the tacho, you're going to be down an odo and speedo too?

Well, I really don't know. I would think that the processor in the cluster gets it's signal from the ecu, but I'm not sure what signal that is and where to connect it to.
I was thinking of soldering tacho out directly onto the tach inside the cluster and cutting the existing circuit to the processor.

Tacho: The cluster processor takes the signal from the ECU and converts it to SIN+,SIN-,COS+,COS- for the tacho gauge to work.
Speedo: The cluster processor takes the signal directly from the gearbox (2-wire VR sensor) and converts it to 50% DC variable frequency square wave for the ECU and SIN+,SIN-,COS+,COS- for the speedo gauge.

Your speedo will work fine as-is. You have to do the tacho output mod and connect it to the proper wire on the cluster harness. On the 2001+, the tacho is NOT driven off the coils, so we can just connect the tacho output to pin 3O on the ECU harness. I don't know about the 99.

Jim

3O is for IAC on a '99, so the big question is what wire do I need on a '99?

Thx Joe, best I could come up with was green / orange in 2K as this is IG- in the diagnostics connector.

You know, I think you're right. I've had black/white on the brain lately as that's the standard tach wire in the earlier cars, but now that you mention it, the grn/org wire at 2K probably is the correct one.

Damn NBs and their modern color-codes... :rolleyes"

I just had a look at both wiring diagramms for the 1999-2000 and for the 2001-2004.

2K at the 1999-2000 is g/o and goes to the instrument cluster and to the diagnostic connector.

3O at the 2001-2004 is also g/o and also goes to the instrument cluster and to the diagnostic connector.

Should be it then...

great, another step closer to MS2E completion on a '99-'00 :)
thx guys