Installing tachometer

[chazchuzzlewitt]

I'd really like to install a tach on my 350 instead of the giant clock if it's not too much of a pain- I've seen a few 116 instrument clusters on ebay etc that have the tacho with them- what parts would I actually need (apart from the tach itself obviously) to make it work?

cheers.

[116.025]

I added a tach to both my 280SE and my 280SEL since they came with the clock instead of the clock/tach combo.  All you need is the tach itself(as you said, obviously), and two wiring ends that fit onto the tach, and a piece of wire with an end on it to add to the harness next to the ignition coil.  When I get home from work I'll post a pic of the under the hood shot and explain things in a little more detail.  The hardest part for me was running the wire for the tach signal through the firewall, so all in all, it's pretty easy.  Of course, I'm assuming you don't want to go the long way and actually install a factory harness with tach connections, because that wouldn't be simple at all...

It's nice to be helping instead of just asking for help 

Hey Chazchuzzlewitt, I uploaded the pics to the gallery under garage, I'll explain in more detail later, something's come up for the moment.

[chazchuzzlewitt]

thanks for that... now just to try and win this ebay US auction and get it shipped over...

[116.025]

Ok, so first is the under the hood shot...



The signal that the tachometer uses comes from the terminal on the right, as noted in the picture.  Since yours is a non-tach car, there will currently be 2 wires attached under the screw on that terminal, which are green and yellow striped.  All you need to do here is attach a third wire(with one of those ends with a hole in it), and route it appropriately through the fire wall.  When I did the 280SE (the one I did second) I routed it through the same grommet as a heater hose, which was a bit more accesible from inside the car than the way I routed it when I did the 280SEL.  Also, a bit of experience on the 280SEL quickly taught me it is far better to route the tach signal wire underneath all of the other stuff than over, so you don't bump it when you do other things. 



This is the shot of my rig inside the car.  To make the connections to the tach, I cut some ends off of a 116 I use for parts, and used a wire nut to fasten it to the dinky wire I used for the tach signal.  There can't be much current in the tach signal, since I used a single strand out of some phone wire lying around...For the 12V power, I borrowed another end and stripped some of the insulation back and after shoving the wire into the terminal that powers the clock, I pushed the whole thing back onto the clock.  There's enough room since the female end has a circular space. 

A fairly simple job all in all, but one tip from experience...either disconnect the battery or the fuse that has the clock on it...I popped a fuse when I put the tach in the 280SEL...the 12V wire for the clock flopped around, and since I had the key in the ignition(so I could listen to some tunes while I worked  ), I saw a little arc as the current jumped into the key, knocking the fuse out of the slot.  Being stubborn as I am sometimes, I popped the fuse back into place and kept working...a few minutes later, the clock wire hit a metal cross member that is normally behind the instrument cluster, this time actually blowing the fuse...so, having finally learned my lesson, I removed the negative terminal from the battery...

[chazchuzzlewitt]

is this the correct tach? it came off a diesel model but I presume it's the same design for the petrol ones...

[s class]

Chaz,

As far as I know, the clusters for the different models differ primarily in where the red line starts on the tacho, and the location of the change indicators on the speedo.  Although the change indicators seem to have been marked only for some markets. 

See these pics of my 280SE cluster. 





sorry - a chance to show off my mileage 

[116.025]

is this the correct tach? it came off a diesel model but I presume it's the same design for the petrol ones...

I'm practically certain that's not from a diesel, diesel tachometers have no redline on them.  But otherwise, I think the tachs will interchange, the redline will just be in different places, like Ryan said.

And speaking of mileage, Ryan, I think I've passed you now...my odometer turned 425,000 kilometers yesterday.  Of course, until I get my OM615 reassembled, my 280SE is what I'm driving, so it's getting at least 120km a day just for me to commute to work, and upwards of 200km/day if I do anything fun after work.

[s class]

Cool chad,

As of yesterday I'm at 424 xxx.  But since its no longer my daily driver I only do about 100km a week 

[robgee]

Hi Chaz looking at that instrument cluster its redlined at the same spot as my 450se so I would presume it came from a 450.
regards,
Rob

[116.025]

Cool chad,

As of yesterday I'm at 424 xxx.  But since its no longer my daily driver I only do about 100km a week 

I was thinking I remembered you commenting that your W140 was your daily driver, and that there were financial disadvantages to driving something that wasn't your daily driver.

The good thing about 100km a week in that it's better than no 116 at all...(though that's probably not all that great of a consolation... )

[dudu]

I'd really like to install a tach on my 350 instead of the giant clock if it's not too much of a pain- I've seen a few 116 instrument clusters on ebay etc that have the tacho with them- what parts would I actually need (apart from the tach itself obviously) to make it work?

cheers.

Hi. Almost all tachs have some numbers on their back showing the kind of engine ( 6/8 Zyl, 4 Tak ) they are designed for.
So, in case you need some of them, ask the ebay seller about those numbers.

I replaced mine a couple months ago, it was as easy as 116.025 showed.

Ahhh, just a suggestion. You will need to open the instrument cluster... so , it would be a good time for cleaning and repainting needles.

This is mine just after cleaning up.



Regards.

[BAR]

Installing a Tachometer is not a problem as you have probably gathered by now.

Make sure that you obtain the correct one for your car: an 8 cyl tacho' is what's needed in your case.  Any others will not give you a correct reading of the engine speed.

[oscar]

Ahhh, just a suggestion. You will need to open the instrument cluster... so , it would be a good time for cleaning and repainting needles.

This is mine just after cleaning up.

dudu, that looks fantastic.  Something I never considered.  Yet another detailing item to add to the things-to-do list. 
Anything special you used to repaint needles?

[oscar]

Hi fellas,

Whilst I'm watching my tacho fail more often than not, Ive been thinking about getting another one whilst I work on my original. 

Two questions

What's this one from?


The seller says it suits 8 cylinders 350-450 including a 6.9 but it starts at 300rpm, not 500 like mine and all the others pictured.  Also my redline is around the 6250rpm mark unlike this one which is the highest I've seen.

Secondly, does the oil pressure line simply unscrew from behind the cluster?

[chazchuzzlewitt]

I just sold my 350 before installing the tacho I got on ebay- is it true I'll need a different one for my 280 6 cyl than the V8 engines?