Customer had me get him a dakota digital dash for his 71 cuda. Have it all wired up but the tach does not work. Been on tech calls with them. Not able to make it work other than testing it. Testing it involved taking the speed sensor that mounts in the speedo cable. Removing that and mounting a drill on the needle for the speedo into the transmission. Then taking the power wire and the input wire from that cable. Putting power to that from the main box for the system and hooking the input wire into the tach port of the box. Running the drill then puts the signal through the cable into the box which then sends the signal into the cluster to move the tach needle. Pretty simple operation to verify the tach and box all are functioning. The way the tach is supposed to be hooked up is one single wire from the negative side of the coil into the main box which then should run the tach in the cluster. Have it set up that way and nothing works. Tried a new coil nothing. Car will start up and run no issues at all so my thought is should not be any reason the thing would not function. Start the car up and all the rest of the gauges work and function the way it should. Any ideas? I have not tried a separate tach yet. Have the original ralley gauges that I might try but not sure if the tach worked before or not. The dakota digital set up does not rely on anything from the original car except that it is wired into the turn signals and the brake light and fuel sending unit. The oil,speedo and water all get new units installed in the factory spots and separate wires provided by them that plug into those spots and are wired into the main control box in designated spots. Everything is clearly labeled. When I was installing everything I labeled the wires for what they were for along with color coded to the way it is labeled on the main unit. The cluster gets 2 supplied wire sets that plug into the back of the cluster and into the main box. They are idiot proof in that you can't change the locations because of the ends. Only designed to go in one spot. Any ideas?

Thanks

corey