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Big Andy

vdo tacho wiring

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hi all don't know whether ive posted this in the right place sorry if not I'm trying to get my vdo tacho gauge to work with emerald ecu and wiring chassis ive been at it 3 weeks + and still carnt get it working 

I'm open to any ideas 

many thanks 

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When I wired in mine, I had to use a "pull up" resistor - will do a search and see if I can find the details, but if you do not have a resistor between two of the terminals, then this might sort it!

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oh right ok chris that would be good info if you can find it cheers mate

 

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Found it! Thanks to a @Dave Eastwood (Gadgetman) - Club Secretary post - quote:

MBE/VDO fix was a 1k resistor across the green +ve feed to the tacho and the black/white signal feed coming from the ecu.

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hi chris 

I haven't got a green and black/white wire 

the wires I have are red black brown and purple 

which I believe that the black is earth

                                      brown is 12v switch

                                      purple is signal wire from ecu

                                      red is speedometer wel that's what it states on the wire its self lol

 

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OK - trying to think back how I did mine - as I now have a different ECU and an AIM dash!

I think I used the ECU signal wire to feed into the loom b/w wire (which on my loom was the old coil feed). The loom had a green (switched and fused live feed) and so I put the resistor between the live and the signal right at the point where it connected to the tacho.

So if you have +Ve, -Ve and signal - the resistor goes between the +ve and the signal. 

Note - if you are using the ECU to provide the +Ve, it may be outputting +5V - and the Tacho may need +12V. On my old MBE - I used (as above) the loom's +12V and the loom's -Ve feeds with only the signal coming from the ECU.

Might be worth a call to Emerald to confirm all this as I wouldn't want you to hook up 12V to something and it then causes issues - after all, ECU's ain't cheap!

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hi ya chris 

ive got a 1k resistor and put it acros the signal wire and the power wire and it still doesn't work have you any ideas mate 

cheers andy

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I presume the tachometer worked with your old set up? Was it a distributor you had before?

How do you mean it doesn't work? No movement of the needle at all, irregular movement...

Have you touched any of the configuration dip switches on the rev counter?

How about the ecu, was it brand new, or is it a swap from another car?

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Hi ya Dave 

Its a new build and the clocks was bought of the forum and the ecu is brand new from robin hood and no I've not touched the dip switches 

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So, if it's an Emerald K3/K6 ecu, it should have a 12 V pulsed tacho output on pin 12 of the ecu plug, feeding to signal in on the rev counter. The rev counter should get power and ground from the regular car loom.

Are you running the ignition in basic "wasted spark" mode? ie firing twice for every normal spark?

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not sure dave we have just plug it in to the emerald wiring chassis is there anyone you know who lives clode to chesterfield lol

 

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I presume the tachometer is getting 12 V from the ignition live feed? Also note, that confusingly, some VDO rev counters show the signal input pin marked as "12 V", whereas, if I remember right, the power pin is just marked "+" (and the ground "-") - These are sepperate to the + & - feeds to the back light bulb(s)

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