WestfieldMX5

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



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 .

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 .

richyvrlimited

iTrader: (1)

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?

WestfieldMX5

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.

Reverant

iTrader: (10)

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

WestfieldMX5

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

Joe Perez

iTrader: (8)

2D, a white / black wire that feeds both the instrument panel and the cruise control computer.

WestfieldMX5

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

Joe Perez

iTrader: (8)

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"

Zaphod

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...

WestfieldMX5

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