Positive earth speed sensor?

OK, after annoying Smiths, Andover Norton & CNW I got my answer.

I thought, incorrectly, that the Smiths speedo could supply 12v + a ground signal to the sensor, this in fact needs to be supplied separately.

I got this from Matt in CNW for the sensor wiring:

Blue - To Positive (battery or common ground)
Tan - 12 volt power, Negative in your case. You can run this together with some other power lead that is fused
Black - To the Speed signal wire from the Smiths gauge, White/Black. So this is the only wire you need to run all the way up to the headlight

I need to now figure out where's the best place to tap into a switched power supply, any suggestions? the MK3 has a standard wiring loom.

I don’t have a wiring diagram handy at the moment but possibly the rear brake switch or horn (last resort) if you want to pick it up from the back of the bike.
Pete

Yup, white wire on the rear brake switch.

Thanks gents, I'll check the wiring diagram and look into using the rear brake switch wiring

jan nelder said:

the sensor with the Smiths speedo I used just needs a lump of metal passing by for a trigger, and is insulated from the bike...just wires into speedo head. Easy calibration too, once wheel rolling radius and lumps per revolution established. (Deer in the yard... it’s what’s watching the deer that will slow you down... or speed you up!!)

Click to expand...

Hi Jan,

I've been taking my time with the speedo install!! I did a bench test of the speedo & could not get a reading from the sensor. To be honest I didn't spend a lot of time testing so I need to go back to this.

Jan, you mention in the above post "just wires into speedo head". Does this mean with the sensor you are using you only have to wire it to the speedo wires only? i.e. it does not need a 12V supply from the battery/switched source?

I used the M8 reed-switch sender, as shown in the link below. Mounted with modified cNw hardware. Wired up as per the instructions. All good so far.

http://www.puca.co/accessories.html

click said:

Interesting, my understanding is that you have two options with the new Smiths electronic speedo's, run them off the original mechanical drive using a sensor that screws in like the old speedo cable or use a GPS signal cable. Are you saying there's a third option?

Click to expand...

Those options are just variations of one principle: The speedometer needs a pulsed (i.e. stepped) analogue signal - I am not sure of the voltage - normally a low voltage signal of 5V maximum.

There are a few variations how to produce this signal, either by a magnetic coil sender type (i.e. transducer), by a magnetic coil receiver type (Hall effect; it needs induction by an external magnet), by a reed switch (which clips a suitably reduced DC input voltage), or an artificially generated pulsed signal.

Smith's electronic speedometers won't accept a GPS signal directly. CAI may supply a "GPS devices that will provide a pulsed input into your speedometer".

-Knut