Smoothing out electrical pulses.

Instructions are in Chinglise so made in china, says not to cut wires and if there are any questions to contact local distributor.

But let’s give it a go.  My interpretation of the supplied information:

The sensing head can be mounted to either the HT cable or the signal cable to the coil. As you don’t have a coil you are restricted to the HT  cable, closer to the plug than the mag.

The drawing suggests you have a three pole plug to connect the sensing head to the meter.  The meter requires a constant live via the red core by using a “scotch lock”,picking up the supply from the battery.  

Now the red/ green and brown leads from the sensing head:

RED: from sensing head is connected to brown cable “scotch locked”

to a switched supply and goes into the meter head.

GREEN: appears to connect to the BLACK lead going to the meter AND THEN GROUNDED. 

BROWN: connects to the OTHER core (described as RPM signal) going to the meter head.

Possible issue is that there are TWO brown cores involved…if the sensing head connector is a moulded item it should not be a problem.  But if it’s individual items maybe there is the issue.

Summing up, four cores to the meter, one 12v supply, a switched 12v supply, a ground and a pulse signal. 

Good luck

Jon

You could just go all retro and fit a Smiths magnetic or chronometric rev counter and keep the mag, like wot I have done. Or be cheapskate and not bother with the tacho. You don't really need one anyway. It doesn't make sense to do away with the magneto for the sake of a cheap electronic tacho.

Put your switched power supply on to the sensor and check that the voltage appears at the 

disconnected Green core; should be the same.

Now if you have a multimeter with a current range. Set the meter up to read current and connect the green core to one lead and the other to ground. You should see a low milliamperes reading. No different to leaving a coil powered, it gets hot.

if you only have a voltage range you can do similar but just keep measuring the voltage while you dab the green core to earth.  The voltage should dip slightly as you connect to ground.

 The whole set up is the reverse of coil ignition, a primary and a secondary.  The switching high voltage to your HT lead is inducing a low level voltage into the sensor coil which then triggers the rev counter head.

Jon

You can modify a standard timing case. As impoverished students, we would build up the boss with araldite and drill the appropriate holes. More sophisticated owners would actually build up the case with weld. Posh or what?

Does the manufacturer state it is suitable for Positive Earth?  Who is the manufacturer Neil?  I  looked at Smiths Classic but don't see your wiring diagram.  When electronics are involved the polarity of supply can be an issue.

 The Smiths documentation states for Negative earth only...

Jon

Neil, the information is in byte size.   The bigger picture would help.  I attach an interpretation of what you have asked for to date.

Cheers

Jon

To get a GPS sensor that fed a digital speedometer to work I had to add a resistor and also feed it with full fat 12v not the 12v within the digital speedo which was current limited.

Neil, just note that when you get the installation to function consider protection from over current and ease of disconnection.  

Should modification from OEM spec be required (as per JH) feedback to supplier so they can improve the product.

Jon

You could fit the offending tacho to something with battery ignition to see if it works.

These sensors normally run at 5V internally, they either have a voltage regulator inside to drop 12v to 5v or the speedo/tacho head has a live 5V feed. If you have a sensor expecting 5v and its fed 12v then it will be fried.

33 ohms was the resistor specified for my GPS sensor, which is odd considering its stated input voltage tolerance of 6 to 32V.

Hello,

wonder if it makes any difference which way round the sensor fits to the ht lead.  looking at it in the photo the plug is left of the sensor when it should be to the right side. according to the diagrame. i dont know. just thinking of how a timing light works and has a directional arrow on the sensor.

Barry