Black is obviously the ground/earth lead, white is the back light illumination and the red needs a connection that is only live when the ignition is on. Just swap it to the +ve side of the coil and see if it works. I am getting conflicting info on where to hook it up (seen both +ve and -ve!!?!) but your truck did come with a factory tacho option which means there is a trigger wire in the instrument socket in the back of your dash cluster. It may even have the 'trace' indicated on the back of the instrument cluster which would mean all you need to do is bridge your tacho into it and you're set.