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Tacho 101

Started by gavin116, 17 February 2012, 08:07 PM


Parts to acquire:

Rev counter and clock that is red-lined from 5800 RPM for the V8 models (6.9's, SD's and 280's all have different tachos)

Two lengths of wire, two different colours (green/yellow and black/red if you want to be totally original)

Cable sleeve

Ring terminals x2

Round pin bushing for rev counter plug x2 MA003 545 26 26

Cable connector for rev counter plug MA008 545 37 28

Plug for rev counter plug MA008 545 38 28

Optional parts:

Bulb for festoon lights – small x2 MN072601 012230

Bulb for warning lights and festoon – large x8 MN072601 012240



Solder the wires into the round pin bushings.

Clip the two parts of the plug together incorporating the bushings.

Orientate them so that the power cable feed (black/red) is in the bottom pin and the pick-up feed (green/yellow) is the top pin.  The plug has a notch so that it can only fit one way. (I did not use the 'original colour scheme' for my wiring.)

Slip a cable sleeve around the wires to give a factory wiring harness finish.

Disconnect the battery.

Remove the instrument cluster.  Just pull it forwards from around the edges, as it works it way loose, you can then begin disconnecting the peripherals from behind. That will be a power wire to the clock, one to the RHS warning lamp bank for the brake pad wear indicator (some cars have additional warning lights, up to two), the pick-up for the cruise control if fitted, unscrew the speedo-cable, and now you should be able to ease the binnacle a little more forward.  Disconnect the oil pressure line (8mm, or was it 10mm) take care not to break it or start the car if it is not connected! And now lastly remove the multi-plug and the earth wire.  You should be able to free the binnacle now.  Placing a little masking/insulation tape over the wood will protect it from damage when you remove the binnacle. 

The good Doctor Bill has kindly done the "Instrument cluster removal 101" check the link here:

Carefully disassemble the various rear components of the binnacle, you have to remove all three.  So, at this point it may be worthwhile to replace all the bulbs and give it a good clean with glass cleaner.  Do not be tempted to clean any of the dials, only do the poly glass.  Reassemble with the new rev counter.  (Test that the clock adjuster and the trip meter reset knobs are correctly seated and work.)

Carefully cut a hole in one of the nipples of the main vacuum and electrical inlets, and pass a fish-tape through this opening into the interior of the car.  Attach you pre-made cable and pull it from inside the car into the engine bay.  Leave a little slack to easily connect it to the instrument binnacle.

Reconnect the binnacle in the reverse order as above.

Route the pick-up wire in its own sleeve, and route it along the firewall, and down the left of the fender towards the coil.  Crimp on the ring connector, and now connect this to the "green" side of the bipolar connector.  (And yes, I have finally delt with the rust beneath the ignition module, just don't have a new picture.)

Open the fuse box, remove the relays and now you can remove the screws that hold the fuse rails in place, and connect the power cable for the rev counter to fuse number 4.  Route this wire through one of the nipples to the front of the fuse box, again you may need to cut one open, and as for the pick-up wire, crimp a ring connector to the power wire and secure to the back of the fuse rail.  (In the picture below, use fuse 4 on the bottom fuse rail, and at the top of the picture, the large grommet that needs to have a nipple cut to pass the wires into the cabin.)

Now reconnect the battery, you will note from setting the time on the new clock, that this is indeed not a quick job.  Start the car and 'voila' the tacho works! :)
1979 450SE "Mrs White"
2022 Touareg-R 3.0TSi Hybrid


Nice post and good job.

Boogity, Boogity, Boogity, Amen!


Excellent work Gavin. 

Wish I had it this a few years ago when I got the wires around the wrong way once and fried a tacho for a 280 :(
1973 350SE, my first & fave


Great job.

Thanks for the effort - I know what it takes to illustrate and explain a job.


TJ 450

Well done!

One of these days I'll do this on my 280S... I'm reliant on the max speed indicators as on the speedo face, and would rather see the tacho for peace of mind.

1976 450SEL 6.9 1432
1969 300SEL 6.3 1394
2003 ML500


Fantastic explanation, sir. Thank you.
1975 Euro 350SE
1992 Euro C124 300CE-24 Sportline 5-speed Getrag
2002 R170 SLK320 6-speed
1986 190E 2.3-16 - sold
1987 W126 300SDL -sold
1994 E420 - sold
1968 W108 250SE - sold
1962 W111 220Sb - sold
1969 Porsche 911T, 911S
1980 911SC
1974 Citroen DS23


Great post, am going to try this on the weekend! Will update with how I go!
With the amount of cars I own, some call me crazy. To them I say: I'm just in love.


Hi Titanbenz

I did a Tachometer 101 update/revisit on my 'vlog' too. Here's the link:

It should be straightforward really, a decade ago I got a lot of help from Koan and Joe Brasile and thought I would share what I gained. Unfortunately, so many picture links are broken, I have had to do some 'revisits'/updates.

Kind regards,

1979 450SE "Mrs White"
2022 Touareg-R 3.0TSi Hybrid


Hi Gavin

It's amazing to see people still visiting this forum after so many years. Koan especially was a wonderful and generous member and I am very grateful for all his help and support back when I started getting to grips with my 6.9. Your tachometer write-up is brilliant and will hopefully help enthusiasts for many years to come.

Have you emigrated to Spain now? I'm still in Blighty, not too far from Wapping.



I recently purchased my W116 450SE and added it to the W126, W140, W220 and W221 stable mates that I own. I am glad that this forum is still active. The knowledge and help that you guys provide is invaluable. Thank you again, much appreciated!
With the amount of cars I own, some call me crazy. To them I say: I'm just in love.


Hi Adam

We have indeed emigrated to Spain, and enjoy living here. The people are friendly and the weather is good, and I'm slowly getting to grips with the language. We are due to take possession of a new flat in Southwark next week all being well, which will give me a London base again.

Mrs White still lives in Horsham, but sadly I have hardly seen the car since Covid. However this year I do plan to have a bit of maintenance done: new timing chain, guide rails, sprocket, oilers and chain tensioner. I also need my fuel gauge reserve light seen to (I don't want to get stuck without fuel again), and to replace the RHS wiper motor on my headlamp, as well something to stop my fan-belt from squealing. If I recall correctly the current alternator is not the correct one for my car. ::)

I also need to enquire about the fuel system, as increasingly it's getting harder to find E5 fuel, the norm in Spain is E10 and I have seen E85 in France! The rubber components in our fuel system would not tolerate that sort of ethanol content I'm sure.

I hope to do a long trip in Mrs White at the beginning of August, either to Scotland or the Continent: France, Germany, The Netherlands or Belgium. It would be good to meet up again perhaps in August.

Till then, keep 116ing!

1979 450SE "Mrs White"
2022 Touareg-R 3.0TSi Hybrid


Here in Colorado we have only had 10% alcohol in all Gasoline available the last 20 years.  The cars all run fine with it.

Small 2 cycle engines hate it though.
'68 250S
'77 6.9 Euro
'91 300SE,
'98 SL500
'14 CLS550,
'21 E450 Cabrio