For the aftermarket tachs you need to wire the signal wire to one of the negative wires (there are 2) going into the ignition coil. IIRC it is black wire/blue stripe.

Hector 2003 Rally Red Mitsubishi Evolution VIII 257HP/259TQ 2005 Lapis Blue Mazda 6s RET: 00 Cabernet Red Ford Contour Zetec ATX SUPERCHARGED 160HP/141TQ