15 replies to this topic

[Dan6061]

Bought a little Tachometer off eBay, and have been trying to wire it up.
My friend wired the green wire (on the tacho) to a white cable that I'm pretty sure goes to the coil.
Then the red cable wire linked to a black/white wire?
The car would start up fine, then when we earthed it, the car would cut out, but the tacho would light up?

Oh, and the tach doesn't have a white wire like others do?
Help.


EDIT: Only just noticed the search bar (nooob) sorry!

Edited by Dan6061, 30 November 2007 - 03:13 PM.

[Guess-Works.com]

You need the wiring diagram for the tacho before you connect it, as the likelyhood is you'll damage the tacho if not done correctly...

There's proably 4 or 5 wires exiting from the back of the unit, one will be earth, one will be the 'sense' wire, one will be an ignition live 12v line and the other for illumination...

[dklawson]

Generic tach wiring (non-Smiths)

Black = earth/ground
Red = +12V (SWITCHED)
White = Illumination
Green = Sense

Earth is obvious. Red... look for a switched source behind the dash... use your car's wiring diagram. White (lights) connect to the dash lights wiring (typically a Red/White wire in Lucas color codes). You MAY find a white/black wire behind your dash. This goes to the coil (-) terminal. Connect this to the Green wire on the tach. If you don't find a white/black behind the dash, pull a new Green wire all the way from the tach to the coil (-) terminal (the connection that has a wire going to the distributor).

EDIT: Sorry, I went back and noticed you said you had no white wire on the tach you bought. Post a picture of the front and back of your tach and/or give us its make and model number.

The wiring you've done so far is obviously incorrect. First, the white wire going to the coil would be going to coil (+) (full +12V), not coil (-). The red wire probably should be connected there, not the green wire. By connecting the red wire to the white/black wire, you're powering the tach THROUGH the coil. When you connect the tach to earth, power is continuously flowing through the coil... defeating the points in the distributor. In effect, you've created a kill switch with your tachometer. Try the following wiring. Red wire to the white wire going to coil (+). Green wire to the white/black wire. Black wire (or tach case) connected to earth. Still... post pictures and identification for the tach if you can.

Edited by dklawson, 30 November 2007 - 03:23 PM.

[Dan6061]

There isn't a white wire...
Guessing it doesn't really matter?

Right, so instead of having the green tacho wire going to the B/W wire, take it straight to the coil terminal?
Sorry to be a noob, but by 'switched' source, do you mean like, the ignition?

Haven't got the instructions with me here, but i'm sure it says wire the red to the ignition +? (Pretty sure my mate did that...?)

Edited by Dan6061, 30 November 2007 - 03:20 PM.

[dklawson]

Sorry, we're both typing at the same time. Please read my edited post above for a suggested change to the wiring. Yes, by switched I mean a power supply that is "off" when the ignition key is removed.

by the way, it sounds like your tach light will be ON anytime the tach is powered up. (The internal light is probably connected to the red wire and to the gauge case or black wire).

EDIT:
See the attached picture. In your case, assume the red and white wires are connected inside the tach. You can connect the red wire to a switched +12v supply as shown... or... since this is a Mini, connect it to the white wire going to coil (+) since that wire IS switched power from the ignition switch.

Attached Files

•  stdwire.gif   17.68K   38 downloads

Edited by dklawson, 30 November 2007 - 03:36 PM.

[Dan6061]

Right then, followed your wiring instructions, and now it lights up when the car is on, and it doesn't cut out or anything.
At first the dial goes round, then back. But doesn't move when I rev the engine?

Will have to get pictures another time as i'm off out in a minute...

Link to eBay (where I got it)

[dklawson]

Well that's curious. Look at the pictures in the auction, particularly the side view half way down the page. If you look just below the measuring scale in the picture you can see 4 wires: red, black, green, AND white. (The white wire is just visible laying on top of the other wires at the 1" mark).

Did they send you NO documentation with this? The listing says it's new. I would expect anything new to come with some paperwork no matter how simple it is.

The needle going all the way around and then back implies that this is a stepper motor driven gauge and it's executing a self-test. That is normal on a lot of modern aftermarket gauges. The fact that the gauge is not responding to you reving the engine is not a good thing. Hopefully your first wiring connections have not damaged the gauge. I suggest you write the seller and tell them how you first connected the gauge and ask them if it should still be OK. Also, if there was no documentation supplied with the gauge... ask them why wasn't there any?


by the way, you got me to searching on eBay U.K. (much more fun than working) See this listing:
http://cgi.ebay.co.u...1QQcmdZViewItem

That's a 2" VDO tach. VERY bullet proof if not a bit small. These will fit in the dash holes of center binnacles.

[Dan6061]

With it I got an A4 page of instructions, that says where to connect the Green, Red, and Black wires.
No white one?

Guessing that's what you mean by documentation?

[dklawson]

Where did the instruction sheet say to connect the three wires on your tach?

[Dan6061]

Instructions say:

1. Disconnect the negatice battery cable.
2. Set the cylinder switch..................
3. Choose mounting position.......
4. Look before drilling...etc...
5. After mounting it, connect as follows:
Black goes to a good ground like the negative battery terminal or a good chassis ground.
Red goes to a +12 volt source that is energized only when the key is in the 'on' position.
This can be at the fuse box or the igniton switch 'on' position.
Green goes to the vehicles tachometer signal source. You must consult your service manuel to ensure the proper connection. If using an aftermarket ignition system be sure to follow the mafucaturer's instructions. Failure to do so could ruin your tachometer.

Wiring Installation.

RED - 12v Ignition switch (+)
BLACK - Engine ground.
GREEN - On standard ignitions GREEN wire attatches to coil negative (-) OR electronic ignitions, such as wire attach to tacho termincal.

[Dan]

I imagine that the way it was wired up and run initially has destroyed it internally since it is now correctly wired and not working.

[dklawson]

I imagine that the way it was wired up and run initially has destroyed it internally since it is now correctly wired and not working.

I agree. The wiring mistake really shouldn't have destroyed the gauge on a well designed/protected instrument. However, what may have happened in this case is an over-voltage spike. The points are protected by the condenser (in the distributor) from the voltage spike that occurs when the points open. Sine this tach's red power wire was connected (effectively) to the coil (-) terminal and did not have such protection, its VERY likely that it received a severe over voltage spike when the points opened. This probably fried the circuit.

I'm afraid with the disclaimer they gave about wiring mistakes damaging the unit you really don't have a lot of wiggle room to ask for the vendor's help replacing/resolving this. I also suspect shipping the dead unit back to Hong Kong wouldn't be cost effective. Keep watching eBay for nice looking USED tachs. I think you'll find some cost effective ones closer to home that will work quite well. Keep the link I posted above with the color codes for future reference. You can see that even the Chinese tach utilizes the same standard use of the red, green, and black wire colors.

[Dan6061]

Daaaaamn.
Ah well, was my friend that wired it up wrong, he can give me the money for it.

Got another problem now.
Wired the black wire up straight to the negative battery terminal for a good ground, and it all still worked.
But after that, the light that tells me when the immobiliser's on doesn't work, neither does the interior light. =\

Errrmm...whaaaaat?!

[dklawson]

Got another problem now.
Wired the black wire up straight to the negative battery terminal for a good ground, and it all still worked.
But after that, the light that tells me when the immobiliser's on doesn't work, neither does the interior light. =\

That may be totally unrelated. Completely remove the tach and all the wiring you added for it. If the problem goes away, assume it's something else weird with the tach. If the problem persists, it's not likely to have been related to the tach anyway. When it comes to things like the immobilizer, others will have to help you.

[Ethel]

If you disconnected the battery as per the instructions you had that may have tripped the immobiliser. I expect there's a way of resetting it.