by lofty » Mon May 09, 2022 9:05 am
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