Tach wire is yellow/black on the unit you'll want to run it under the hood though a safe location, through the firewall and hook it to the white wire on the distributor. Tach programs differently depending on how old the unit is. The dome light is definitely a factory thing, compustar will only hold lights on 45 seconds if hooked up. If i was you I would take it to an authorized compustar dealer and pay to have everything setup the right way you want.