TB42 to TD42 - Tacho Not Working.

[jaztaz]

Hi there,

Having a lot of dramas trying to get my tacho working, ready to pull my hair out.

I have an 89 GQ that had a TB42 in it but was converted to a 1993 TD42 not long before I bought it.

I have searched a few forums & tried all the suggestions that I could find but still to no avail.

Here's where I'm at -
Have installed the tacho gauge from a 96 TD42 into the 89 TB cluster. I noticed the 96 gauge has 3 securing screws instead of the 4 that are in the 89 cluster. The 'D TAM' screw is missing from the 96 gauge. Is that going to present problems? Is the 96 gauge compatible with the 89 wiring? I would assume the 96 gauge is updated from the 89 cluster as it has white font & graduations instead of the yellow from the 89.
There are a blue wire & a green wire coming from the timing cover mounted tacho sensor. I have earthed these both (not at the same time though) & run a bridging wire from the remaining tacho sensor wire to the yellow/black trace wire that goes into the cluster with no results other than swearing from me.

If there is someone out there that has first hand knowledge of how I can rectify this I would love to hear from you please.

Thanks Jaz.

[threedogs]

pretty sure Yendor will have your answer,

[taslucas]

Diesels get their tacho signal from a different place than petrols so maybe it's the engine side of the wiring you should be looking at?

FanTapstic!

[jaztaz]

Diesels get their tacho signal from a different place than petrols so maybe it's the engine side of the wiring you should be looking at?

FanTapstic!

Yep, that's right.

TDs have their tacho sensor mounted in the timing cover, reading from the cam gear I would assume.

TB tachos are signalled from the negative side of the coil.

[Yendor]

The tacho sensor needs to be connected to pins 11 and 12 at the instrument cluster not earthed.

I don't think the later model tacho should cause you any problems. To check, just follow the tracks from pins 11 and 12 and confirm they connect to the tacho gauge in the instrument cluster.

If you are still using the TB42 engine harness you will need to run a wire from the tacho sensor into the instrument cluster and connect it into pin 11.

The yellow wire with a black trace should already be connected to pin 12 at the instrument cluster, you will just need to extend it from where the coil was to the tacho sensor.

[taslucas]

So are the diesel engine wires coming from the timing cover compatible with the petrol engine wires coming from the dash cluster? is it the same signal? Just guessing here lol

EDIT: YENDOR is here, Ill stop guessing and let the master do his thing

[jaztaz]

The tacho sensor needs to be connected to pins 11 and 12 at the instrument cluster not earthed.

I don't think the later model tacho should cause you any problems. To check, just follow the tracks from pins 11 and 12 and confirm they connect to the tacho gauge in the instrument cluster.

If you are still using the TB42 engine harness you will need to run a wire from the tacho sensor into the instrument cluster and connect it into pin 11.

The yellow wire with a black trace should already be connected to pin 12 at the instrument cluster, you will just need to extend it from where the coil was to the tacho sensor.

Thanks Yendor,

Yellow/black trace does go to pin 12 & 11 is empty.

Can I run a wire directly to the rear of the cluster & use a crimp on eyelet to connect it to the track of pin 11 or do I need to source a pin & install it into the plug?

Also, does it matter which of either the blue or green wires from the sensor connect to either pin 11 or 12?

Will try this weekend.

Thanks Jaz.

[Yendor]

So are the diesel engine wires coming from the timing cover compatible with the petrol engine wires coming from the dash cluster? is it the same signal? Just guessing here lol

EDIT: YENDOR is here, Ill stop guessing and let the master do his thing

It's not "just guessing" it's what this forum is all about, people putting ideas forward to try and help other people out.

So don't stop.

[Yendor]

Thanks Yendor,

Yellow/black trace does go to pin 12 & 11 is empty.

Can I run a wire directly to the rear of the cluster & use a crimp on eyelet to connect it to the track of pin 11 or do I need to source a pin & install it into the plug?

Also, does it matter which of either the blue or green wires from the sensor connect to either pin 11 or 12?

Will try this weekend.

Thanks Jaz.

Hi Jaz,

Yes you can connect the wire directly to the cluster, either by using a crimp eyelet or by soldering onto the PCB.

It shouldn't matter which way the wires are connected at the sensor, though it's always good to have it connected just like factory.

Hopefully someone could have a look at their GQ TD42 and tell us if the Yellow wire with a Black trace is connected to the Blue or the Green wire at the sensor.

Cheers Rodney

[jaztaz]

Hi there,

Having a lot of dramas trying to get my tacho working, ready to pull my hair out.

I have an 89 GQ that had a TB42 in it but was converted to a 1993 TD42 not long before I bought it.

I have searched a few forums & tried all the suggestions that I could find but still to no avail.

Here's where I'm at -
Have installed the tacho gauge from a 96 TD42 into the 89 TB cluster. I noticed the 96 gauge has 3 securing screws instead of the 4 that are in the 89 cluster. The 'D TAM' screw is missing from the 96 gauge. Is that going to present problems? Is the 96 gauge compatible with the 89 wiring? I would assume the 96 gauge is updated from the 89 cluster as it has white font & graduations instead of the yellow from the 89.
There are a blue wire & a green wire coming from the timing cover mounted tacho sensor. I have earthed these both (not at the same time though) & run a bridging wire from the remaining tacho sensor wire to the yellow/black trace wire that goes into the cluster with no results other than swearing from me.

If there is someone out there that has first hand knowledge of how I can rectify this I would love to hear from you please.

Thanks Jaz.

The 'D TAM' bridging screw that secures the tacho into the cluster is run back to where pin 11 is in the plug. Unfortunately this is missing from the later model gauge.

All I can think of at the moment is that the pre 93 gauge had the 4 securing screws (unlike post 93 with 3) thus enabling sensor signal to be fed to the gauge via pin 11.

If in the near future anyone has the cluster out of their pre 93 model could you please take a pic of it for me to confirm the above.

Thanks Jaz.