Ok about a year ago we paid an auto electrician to fix up the lights and dash, specifically the tacho in my ute and they pretty much did nothing and charged us a buttload.
so today i decided to have a go at the non working tacho sitting in the dash and the first thing i realised was that there was no ground coming off the tacho and that the loop wire was just bolted directly to the tacho off the coil.
The positive was taken off the ignition knob thing on the instrument cluster.
I ran a ground wire and ran the cable off the coil looped through the tacho and to the nearest black white striped plug and fired it up.
The oil and charge lights lit up on accessories, the tacho jumped around and the engine kicked over but wouldnt start and i noticed a funny smell and a tiny bit of white smoke coming from under the bonnet.
i put everything back to where it was before i mucked around and it still wont start so what the hell did i blow up?

and did i wire the tacho up properly?

The 'loop' is just that ..nothing fancy ..it's wire.

It's purpose is to 'detect' the pulses from the (edit: positive coil) wire. No voltage is applied to the 'loop'.

I bet that you've created a short circuit. I shudder to think how much of your under dash and ignition wiring looms are now melted beyond repair.

Time to go to a different auto electrician, but it might be easier to get another loom from a wreck, or from a cheap second hand car.

You may have only cooked the one wire, but more likely it was un-fused, and you've either blown the common 'fusible link' (if later utes have this?), or you've blown an ignition fuse. Depending on how you ran your new wiring, will determine what might have got melted when it went white hot.

G'day Old Fart
Mate, I have been having exactly the same issues with my damn Tacho..
No one seems to be able to tell me what to do with the loop behind the tacho.
Its ok to say " its just a loop" but some sort of voltage must be applied to it so that the tacho can read the "pulse".
That said, OK so I attach it to the Neg side of the coil... cool...
Where does the other end go ???
I tried the black wire with white trace... did nothing....
I tried earth... did nothing....
I tried taking it back to the Pos side of coil... did nothing....
I can't put it to the Dist ( as has been suggested ) as I have electronic ignition...

Now my head lights don't work ( must admit, they were dicky to start with )
And it won't start..... I didn't smell anything out of the ordinary tho
Mine is in an 81 ute and I don't believe the wiring harness supports it as standard.
As it is unlicensed, it will be a few weeks before I can get it to an auto elec to find out whats going on. If you are still having probs then, I will give you my solution.
In the meantime, if you find out with yours, can you let me know...
Very frustrating huh...

Cheers

Adam

Both sides of the tacho 'loop' go to the same black/white wire.

There is a distance along the wire between the points that these wires are attached to the b/w wire. The points that they join the b/w wire are between the ignition switch and the ballast resistor on the coil.
The b/w wire is the 'ballast resistor 12v' wire from the ignition switch.

Alternatively, you can 'cut' the b/w wire , and put the tacho inline with the b/w wire. Don't crimp the connectors on, until you figure out which direction the pulses need to go through the 'loop'.

eg.

Ignition switch(IGN terminal)---b/w---tacho connector---tacho---tacho connector---ballast resistor---positive on coil.

newer 1200 tachometers take a voltage signal
older 1200 tachometers take a current signal

Loop Type (current signal)



Voltage Type



You can use either kind but the wiring is different. 1200 coupes and sedans have a dash wiring for the Loop.

Wiring diagrams are at Tech: Tacho Wiring

thanks for the replys.

its definately a loop type tacho and the cable that they ran was straight off the coil to the tacho not from the ballast resistor. is it possible ive wrecked the coil or the capacitor on the dizzy or something?

Sounds like you have run 12v to your coil. Do you have points? Check them cause they are likely fried.
Sounds like you wired it correctly except you needed to connect it to the 12v side of the ballast resistor and not the coil side. (that is if you have points)

AS SAID A THOUSANDS TIMES BEFORE
POWER GOES TO + SIDE OF COIL
FROM SWITCH THRU LOOP WIRE ON TACO THEN TO COIL
AS A TRAIL TAKE + LEAD OF COIL
TAKE A WIRE AND CONNECT TO + BATTERY TERNIMAL
CONNECT TO ONE END OF LOOP WIRE(TACO MITE GO RONG WAY IF SO SWOP POWER WIRES ON LOOP OVER)
CONNECT THE OTHER END OF LOOP WIRE TO + COIL TERMINAL
CHECK THAT U HAVE POWER AT TACO WIRES BLACK AND YELLOW
IF CONNECTED AS SAID TACO WILL WORK UNLESS TACO F@!@KED
THIS IS VERY EASY IF U FOLLOW INSTRUCTIONS
IF NOT RING SOMEONE ITS EASYER TO ASK THAN CHANGE LOOMS/PUT OUT A FLAMING CAR
TOMMO 0411797234

I have two ignition knobs on the back of my speedo. can i take the loop off one of them through the tacho to the black white trace wire?

thanks for the help so far my car is running again.

Quote:

If it is ignition 12v you can use it. But you should not connect the other end to the coil positive (if you have points ignition) you need to connect it to the ballast resistor 12v side. ( it will work if you connect it to the coil but your points will burn out quicker )

ddgonzal's pics and link explian it simply;


* B - ground - to back of Instrument Cluster
* YR - IG power - to back of Instrument Cluster
* RG - lights (two lights, two wires. Not shown in photo above) to back of Instrument Cluster
* BW - signal loop - to BW wires in dash harness


The BW loop of wire is the current induction coil. The ends, logically speaking, go in between the IG terminal of the ignition switch and the single-terminal (non-coil) side of the Ballast Resistor.