Tachometer has to be hooked but youll have to tell nelson or who ever tunes it the model of your truck and theyll tune the pulse so it will register right.
Vss also has to be connected and you can either feed the guage thru the drac box or you can use the speedometer output wire from the new harness and do it that way. Check out the obs to lsx conversion thread... redheartbeat has some good info about speedometer wiring. If you have any other questions just ask... were here to *try* to help!