i have a 1968 camaro ss convertible. i want to add the factory (reproduction) tach to the dash. please tell me what parts i need to buy, ie: tach, tach printed curcuit, do i have to replace the wiring harness, etc. i need instructions to install. the car has the center console with guages. thank you.

I have a 69 not a 68 but what I would do is find a wiring diagram for a 68 and just add the needed wires according to the diagram. I purchased my 69 wiring diagram through Rick's or Classic. My 69 tach has 3 wires- one is most likely from the distributor or coil and one - and one +. You just need to find a diagram and trace the wires. You probably need a plug for the back of the tach as well as the lights. Usually the lights are part of the instrument light group so you will need to add a light or two with the correct housings. Since you didn't have any replies, I thought I'd get you pointed in the right direction.

68's used the infamous "tictoc tach" a tach with a clock in the middle. So, it's got 5 wires, add a ground and "BAT" power for the clock. There was also considerable rearranging of the idiot lights. The titac tach has no idiot lights except for the turn indicator. On the speedo side, the brake light stays, the gen light becomes "low fuel".
The dash, console, and lighting harnesses are different between a guage car and a non guage car. The pcb behind the dash carrier is also different. A conversion harness is currently sold to add the guage package to cars that didn't come with it, while keeping the existing main harnesses. The part that don't make sense is, the 68 guage package includes both the console guages and the tac, you couldn't get one without the other.
Shoot us some more details on your car and wiring. I converted mine last year, including modifying the existing pcb and wiring to handle the tach, and using auto meter guages in the console. I can help you do this, but need to know exactly what you are starting with.