Greetings,

I've been considering finding a 6.3 Tach to install in my 280 SE 4.5 dash. It should fit right where the clock is and since my clock doesn't work (and I have a perfectly good clock on my tape deck) a tach would be more useful, and a factory one would be cool.

My question is: How do you hook one up? I assume it is more involved than an aftermarket Sun Tach. There is one on ebay and if I get it, what other pieces are needed?

Thanks,

Michael

The one I have, which doesn't seem to work, has a red lead and a green lead so I assume it's red to 12VDC and green to coil/ignition box.

Scroll down a bit in this thread for pictures.

Michael

__________________
Usta haves '69 250/8, '76 280C, 1971 250C 114.023, 1976 450SEL 116.033
Current have, 1983 300SD 126.120

Positive lead (red) of the tach to the negative side of the coil, negative lead to earth/ground

The last post was a bit confusing... Did you mean the green wire goes to ground? I dont think that is right. The Clock has a ground through the mounting posts, the tach should probably be the same way.....

So is correct scheme Red to -Coil, Green to power???? Im so confused, who has a wiring diagram for this thing?

-Eric

I had mine open, give me a couple of days to dig it up and double check but IIRC, the red was 12VDC and green was signal. You are correct about the case being ground.

Michael

__________________
Usta haves '69 250/8, '76 280C, 1971 250C 114.023, 1976 450SEL 116.033
Current have, 1983 300SD 126.120

OK, I made it out to the garage finally.

The red wire is labeled +V and the green wire is labeled 1TD. I don't know what a 1TD is but assume it's the points or a terminal in the switch gear box.

Michael

__________________
Usta haves '69 250/8, '76 280C, 1971 250C 114.023, 1976 450SEL 116.033
Current have, 1983 300SD 126.120

I have the blue coil with the ignition box and my tach signal comes from the points which feeds into the ignition box rather than the coil which is switched positive. If your coil is directly connected to the points then just hook it up to the -ve side of the coil.
I would try hooking it up under the hood with some wires to the battery to check it works ok before getting busy with the dashboard and wiring looms.

I wanted to send this as an update to my “6.3 tach in a 4.5” quest.

The tach is in and working fine, took about 2 hours

Green wire is neg terminal on coil. Ground is through posts. Red is 12v. I spliced into the switched circuit that powers the other gauges.

The tach is about ˝ inch deeper than the clock. You’ll need a spacer. The guy on ebay sent one, fit perfectly.

I’ve attached a photo, looks like a 6.3 dash without the rectangular clock. As my clock was broken anyway, this will be much more useful.

Thanks for the input

Michael

Attached Thumbnails

 

Where does the spacer go? What does it look like? I'm doing the same conversion, more or less. Do you have any pictures of the spacer?

-Eric

Hmm, running hot there?

Tach looks nice. I would like one for my 4.5 just to know how high my revs are when I'm flying on the highway...

__________________
Current:
2021 Charger Scat Pack Widebody "Sinabee"
2018 Durango R/T

Previous:
1972 280SE 4.5
2014 Jeep Grand Cherokee Limited "Hefe", 1992 Jeep Cherokee Laredo "Jeepy", 2006 Charger R/T "Hemi"
1999 Chrysler 300M - RIP @ 221k

Sorry, no photos of the spacer but imagine a black plastic ring that circles the body of the gauge, is about 10mm deep and 1mm thick. It takes up the space between the dash panel and sits behind the chrome trim on the tach.

The tach body is longer than the clock, and when the mount posts are in position, the tach stick out of the dash about 10 mm. It actually lines up almost exactly with the speedo and oil/temp/gas gauges.

The car wasn't running when I took the photo. It had been shut off for about 5 minutes. It had been sitting in heavy traffic (30 minutes to go 8 blocks) right before. That's about as hot as it ever gets since I flushed the radiator and switched to the yellow zerex and a little water wetter.

michael

It's so nice to see an 'OE' installation.
Several years ago, my local NAPA autoparts store used to stock a nice, but pricey, line of VDO guages.
For about $70, I bought an under-dash VDO mechanical temp guage for my '57 DKW, as the PO had ruined the original guage in the instrument cluster. As I recall, the NAPA-VDO catalog also listed a small tach. I wonder if it's still availible and if it would fit the clock-hole in the Mercedes cluster.

Happy Motoring, Mark

__________________
DrDKW