Tachometer connections

[drivera]

Picked up a tacho from flea bay cheap ( so probably wont work ) it needs a connection, single wire, to the cdi , which wire would provide the necessary signal, Red White or Green ? anyone know please.

[Dazts1]

Obviously I don’t know which you have. But some work completely different to others. I use a krober unit which connects to brown from the loom for its pulse signal.
Another type I use mychron 4 just has a wire to wrap around the ht lead. Post a pic see what type you have. Someone may be able to help.

[drivera]

Its a cheapo chinese tacho with the name KEGE on it , there is a yellow wire that states its the signal wire , guess I could just piggy back it onto each of the cdi wires to try it , just wondered if anyone else had successfully used one ?

[MickYork]

Not familiar with the make but i'd be inclined to wrap it around the HT lead (4 turns ?) as suggested above. If it is a "hardwired" connection type, trying this way first shouldn't cause any damage.

If not, in most cases the red CDI wire is the pick-up/firing signal.

[lofty]

I have played with a number of tachos over the years, with mixed success..
the main types of connection (as stated above) are wrapped round the HT lead (easy), or connected directly to the feed to the coil (not so easy)..
Unfortunately if you have a standard ducati/vespa type CDI, there is no way to get the LT connection, as its inside the black/blue box..

you may get it to work by attaching to the pulse from the CDI (red) but in many cases this is far too weak to trigger the tacho..

if you have a CDI that used a CDI box with a separate coil (or even standard points, coil), you would be able to get a pulse from the (non earth) coil connection, but there are not many of these about..

however, even once you get it connected and working you need to ensure the tacho is calibrated correctly, for lambrettas, it is 1 spark per revolution (although some have 2 sparks per revolution, eg varitronic).. sometimes this can be set on the tacho, but sometimes it is fixed.. however 1 spark is standard for most 2 stroke singles and 4 stroke twins (including harley type V-twins, which is where a lot of these are aimed at), so is not uncommon. if it connects but reads double or half what it should be it is likely the 'pulse setting' is the culprit..

good luck

[drivera]

Cheers Lofty , I was intending piggy backing the feed from the red CDI connector , I’ll give it a whirl and see , I did a few years ago buy a digital tacho designed for ( go ) carts , that had the trigger wire wrapped around the HT lead , was good but the wiring came apart so now u/s