6 replies to this topic

[Pavel]

Okay still no rest with the tach and if it were up to me i'd got rid of it by now and just bought some aftermarket-y one, but problem is i plan on ordering a 3 clock dashboard and i want the 3 gauges, especially since they're in such mint condition.

I need the following 4 connections clearly defined to me by somebody. Please do not refer me to Haynes, as it is useless (i tried every possible way according to the diagrams..)

Tach is from a 1976 1275GT going into a 1990 City (or mayfair) (with no tach as standard)

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[Pavel]

Tach: (appologize for phone picture quality)

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[Dan]

The four terminal tacho is Pre - 76, Could you get a better photo to be sure if it is four or three terminal?

The four terminal has power and earth as you would expect, but it needs to be on the supply side of the coil, so the other two terminals are ignition feed in from the ignition switch, and out to the coil positive supply. This means the ignition feed to the engine, and therefore the ingnition system itself is running through your tacho. Not always a good idea, as an instrument failure will cripple your car. The three terminal tacho has power and earth, and the third is ignition sensing to the negative side of the tacho, running in parallel with the distributor. This system is quite a bit more accurate and responsive.
Even though the 1990 car will probably be pre wired for a tacho, as most if not all were, the wiring will be prepared for a three terminal tacho not four. Changing over would be quite a project, especially as I believe you will have ballasted ignition on that car.

[Pavel]

Looks like a four terminal tacho since on the 1275GT the coil does in fact get its power through the tach!

Any ideas how I can go about wiring this thing into my 1990 mini? As for ballasted ignition or not, I'm not sure if i do have it or not...

Thanks for being the only person on 3 forums for knowing this by the way

[Dan]

If the coil feed on your car is pink and white or the coil is marked 9volt then you have ballasted ignition. I think the only way you could fit the tacho would be to re-wire the whole system as standard 12volt ignition, but you may find that the tacho can read the signal as is, because it would be in the circuit before the ballast resistor, which is the pink and white wire itself. If doing this you would need to be careful not to change the length of the existing ballast wire, which would mean removing it from the ignition switch connector instead of cutting it inline. You would want to make sure the instrument is in good nick before using it to run your ignition system though. Send it to Speedy Cables and they will check it and clean it, which won't cost too much. They might even be able to convert it to three wire operation for you.

You would probably be better going to Mini In The Park 45 and picking up a later one, as it would be a better match for your other gauges.

It is a shame the car you took this from wasn't a couple of months younger, as 76 was the change point for the wiring harness and tacho, even on the 1275gt.

[Pavel]

Thing is, I'm not in UK, so speedy cables is out, and finding a nice Mini Tach is extremely hard around here...

[Dan]

Sorry, hadn't twigged your location.

Best thing to do is probably add a complete new ignition system, to include the tacho. This would leave your original ballasted system in place and un touched to return to if there was ever a problem. Take a feed from terminal 1 in the fuse box, this should be white and the unfused side of the ignition fed wire. Run this through to the tacho and back to the front of the engine bay, run it along the original loom and ty-rap it to same. Replace the coil with a 12volt one, I don't think the points or condenser need changing unless someone knows different. Keep your old coil to go back to if there are any problems, as the 12volt one won't work with the ballast resistor. The other two terminals can be connected to the instrument supply as usual. If the car is pre-disposed to a tacho, then thats great, use the wires you have. Leave the white/black ignition sense wire taped in the loom though, and make sure its terminal is nicely insulated. The wire from Terminal 1 is how I have fitted Magnetronic kits in the past, and works well.
That is if you have ballasted ignition, if not you can just cut the tacho into the coil feed wire from the ignition switch as if you were cutting in an immobiliser. Make it easy to bypass the tacho in case it fails, maybe with a good quality switch. Make sure any connections for the ignition are good and sound though, as intermittant signals can be a real pain to fault find in the ignition. If you're not sure about doing this, or about the condition of your tacho, get an auto electrician to do it.
You won't miss ballasted ignition on Cyprus, as it's primary function is to assist cold starting. The other thing it is supposed to do is extend points life, but that is not so much of a problem with moving heel points sets as you car should have.
I don't know how this tacho will affect electronic ignition systems. Someone else might though?