New VDO tachometer in a 1970 280SEL? - Mercedes-Benz Forum

 
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post #1 of 5 (permalink) Old 10-15-2008, 10:44 AM Thread Starter
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Question New VDO tachometer in a 1970 280SEL?

I have a new VDO tachometer I am trying to install on my 1970 280SEL with the transitorized ignition. I have tried connecting it as the VDO instructions say to the negative coil terminal, but nothing happens. Any help on where to make the read connection to would be much appreciated
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post #2 of 5 (permalink) Old 10-18-2008, 01:53 PM
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I think you have the setup where the negative side of the coil is simply grounded. Follow the wire from the points and you should find a terminal block where it connects to a green/yellow wire from the transistor box. Try connecting the tach there.

Chuck Taylor
Falls Church VA
1998 SL500
1959 220S
1970 280SL
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post #3 of 5 (permalink) Old 11-06-2008, 09:46 AM Thread Starter
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I think you have the setup where the negative side of the coil is simply grounded. Follow the wire from the points and you should find a terminal block where it connects to a green/yellow wire from the transistor box. Try connecting the tach there.
I connected there, but get a bad reading. I even tried adjusting the tach itself but not accurate at all.
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post #4 of 5 (permalink) Old 11-07-2008, 12:53 AM
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What sort of bad reading? .Most mercedes tacho's take the take signal from a terminal ( green wire with yellow tracer ) within the electronic boxes circuit. For older style electronic switching you may need to add a 50 ohm resistor into the circuit to even out the pulses.
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post #5 of 5 (permalink) Old 11-07-2008, 07:06 AM Thread Starter
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Originally Posted by mercmad6.3 View Post
What sort of bad reading? .Most mercedes tacho's take the take signal from a terminal ( green wire with yellow tracer ) within the electronic boxes circuit. For older style electronic switching you may need to add a 50 ohm resistor into the circuit to even out the pulses.
the tach only moved between "0" and "1000" RPM, rather it was revved up or idling. I will take a look at that wiring again and maybe try the resitor too. Thanks!
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