Have just wired in a new 80mm Smiths (Caerbont) Tachometer. Connect it to the negative side of the coil and the car won't fire (no spark).

Disconnect it, car starts the instant i push the start button.

I have also installed it at the same time as I installed a 123 Ignition Distributor.

Has anyone got any ideas?

Cheers

Matthew

Do u have a multimeter? If u hook it up and turn the ignition only to on, there should be 12v on the coil. Perhaps there is a short in the tacho and its taking this rail to ground?

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http://www.youtube.com/user/Hanras

Yep, the coil is receiving 12v with the ignition on. The whole thing works perfect until you hook up the tacho, then it won't fire.

I have gone over the wiring for the tacho about a dozen times and it is all correct. The (built in) light works, you can hear and see the stepper otor start and move the needle when the ignition goes on.

But no spark once the negative terminal on the coil is connected to the input on the tacho.

Anything I should be checking?

Cable colours OK?
This is off the website: http://www.caigauge.com/Gauge_Fitting_Instructions.htm

GREEN - Connect to switched ignition power source.
(+ve) via 3A fuse
BLACK - Connect to ground (-ve)
RED/WHITE - Connect to dash lamp power
BROWN/SLATE - Not used (Hour meter only)

SIGNAL INPUT ALTERNATIVES:-
The circuit diagram shows all alternatives, only one is needed.
WHITE/BLACK - Connect to Tacho output of electronic ignition
RED/BLUE - Connect to negative side of ignition coil (distributor side)

I notice that for the motorsport range the WHITE/BLACK and the RED/BLUE wires are reversed. Maybe check what your book says and compare it against the website. No problems with mine and it is wired to a Pulsar dizzy.

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SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.

Hi Mick,

Yep those are the instructions I have that came with the gauge. I have used the red/blue wire connected to the negative side of the coil. Is this how you did yours?

How does the pulsar dizzy wire in? The 123 simply has one lead to each terminal on the coil.

Cheers

Matt

I'll check my colours when I get home....drove the forrester to work today ...I wanted a CD player

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SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.

is the ignition system cdi (e.g are there points in the distributor or not?)
alot of the older smiths tachos will not run on cdi ignition, a new circuit board has to be fitted within the tacho to suit cdi.
if the tacho is a later model (e.g 1 pulse terminal on back of case) try running the pulse wire from the positive side of the igintion coil
Good luck!

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Hi-Ho Silver LS1275
Charlieeeeeeeee Come to Candy Mountain!

No points in the dizzy.

http://www.tdcperformance.ca

This is Marcel's site on the 123 dizzy.

Any ideas?

alrite that means its cdi, how many pulse terminals there are on the tacho, can u describe it (terminal wise)

lol just so u no this information is actually coming from my father, a qualified automotive instrument techinician, with about 100 years experience

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Hi-Ho Silver LS1275
Charlieeeeeeeee Come to Candy Mountain!

Yeah, connected as described.
RED/BLUE connected to the -ve side of the coil.

Sounds like it's draining the other side down of the distributor to ground. I would check with a multimeter.
I can measure 128 K Ohm (128000 Ohms) resistance on the blue/red wire between it and ground. You should have the same unless you have connected the extending wires up to the wrong colours. Or they are shorting down to ground with a dodgy bit of insulation.

My positive comes from inside the cabin, and the -ve wire goes to ground in the cabin as well. No need to take it any further than the cabin if you can do so.

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SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.

I have the same dizzy and tacho as you and both work fine. I will check the wiring and let you know how mines hooked up.

Mine is connected as follows:

Green - Ignition switch via a 3A fuse
Black - Earth
Red/White - Dash lights
Red/Blue - Negative side of coil
Brown/Slate - Not used
White/Black - Not used

Also the switches in the back of the tacho are set for contact breaker ignition settings as follows:

1 - Off
2 - Off
3 - On
4 - Off
5 - On
6 - Off

Thanks everyone,

This is how I have it wired in:
GREEN - Connect to switched ignition power source.
(+ve) via 3A fuse (straight from fuse box)
BLACK - Connect to ground (-ve) (Directly to the earth point in the engine bay)
RED/WHITE - Connect to dash lamp power
BROWN/SLATE - Not used (Hour meter only)

SIGNAL INPUT ALTERNATIVES:-
The circuit diagram shows all alternatives, only one is needed.
WHITE/BLACK - Connect to Tacho output of electronic ignition
RED/BLUE - Connect to negative side of ignition coil (distributor side) (This is the one I have used, and it goes straight to the coil.)

Just so everyone knows, I have routed all wiring inside the car at the bulkhead behind the fuse box. So the connections are all fairly direct, and they are new wires, well insulated at the connections.

I'll check the resistance between the red/blue wire and the ground tonight.

Mini68, I think our tachos are slightly different. The one you have is the older version according to their website, which has 6 switches including one for CBP. http://www.caigauge.com/tachofitold.htm

Mine is the newer one, and only has four switches:
http://www.caigauge.com/tachofitnew.htm
The newer one only has settings for 2-12 cylinders, and one for if you need a resistance load against the input???

Thanks for the tips though! I have emailed Caerbont and Marcel but no answers yet!

Cheers
matt

Despite the switch settings, it really can only be be that the tacho or it's wiring is draining all that current from the -ve side of the coil down to ground.

This will be caused by either the wire touching ground in some manner, having it connected to the wrong wire at the back of the tacho (as these wires are only very short lengths out of the back of the tacho), or a warranty issue on the tacho itself.

To avoid having too many wires flinging around, I just used a mounting bolt on the tacho as my ground as I have it in a pod mount bolted to the parcel tray anyway. It avoids mixups.

I doubt highly that the dizzy could be affected by the connection of a normal functioning tacho, as the tacho is a passive device and simply "listens" to the current pulses being applied to through the coil. This is similar to you listening to someone else's conversation, you don't have an impact on it at all.

Good luck with the fault finding!

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SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.