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Did I get a dud tachometer?

S

StreetForged

Member
Joined
May 24, 2018
I wired up an Ebay tach to my 1990 240DL last night and I couldnt get the needle to move, though the lights worked. It has a red(power?), white(light), black(ground), and green wire(Tach), which I've hooked up in the corresponding way:

-Red wire i tested on both the battery and on what i believe to be the positive post on the coil

-White is spliced onto one of the fuses on the fusebox under the steering wheel, can't remember which

-Black is grounded to a bolt on the chassis near the fuse box

-Green I have tried hooking up to both the blue wires on the coil, and the red and white wire behind the gauge cluster that I believe is for the OEM tach?

I have done some research to get this far, but at this point I'm just assuming the tach itself is a dud. I have installed two of these on other cars before and haven't had this same issue, but I could have done something wrong and figured someone else might have more of a clue than me.
 
Maybe the tach uses a five volt digital signal instead of the coil switching signal like the stock tach? The white/red inside the dash comes from coil terminal 1 to provide the signal to the tach.

Red is power on your tach? It should go to a switched fuse like fuse 12 or lower.
White? Illumination? should go to one of the wires for the center console lighting.
Black to a good ground.
Green is your signal wire? Then that should connect to the white/red inside the dash. If the tach works with the coil switching signal. Like I said you may need a different tach if it doesn't use that type of signal.
 
daijoubanai said:
lol that is true. I would just find a stock 240 tach if it were me.
Click to expand...

I would have done that but I couldn't find one for less than 100 bucks so I figured whatever, I'll keep the clock and spend 15% of that and get the same feature, but here we are...
 
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