Blue wire coming straight out of the dizzy is your feed to the rev gauge (thats how we have our hotrods wired anyway). Thats the quick and easy solution but id imagine the loom in the back of the clocks would have a feed for a tacho too, regardless of whether your car came with one or not. Afaik, the feed from the ecu is pin 2 Blue/grey tracer .....it was in the march k11 loom i was working on not long ago.