If your car truly has been changed to 12 volts, you do not need something like this. It is possible to retain the original coil in a 12 volt conversion , usually by adding something called a "ballast resistor". This brings all of the voltages in line for a 12 volt system, allowing a regular 12 volt tach to be wired up normally. This is assuming that your car has been wired up negative ground. The polarity is almost always changed from positive ground to negative ground when a vehicle is converted to 12 volt operation, but you never know what might have happened in the past. Check your polarity first, and if you car is negative ground, you're good to go. If it's positive ground..... Well, get back to me and we can go from there. One last thing here; If your car all of a sudden starts to run badly, missing, etc. The first thing to suspect is the coil. Most people don't understand the current and resistance requirements to make the ignition work properly. If not set up just right, you'll end up with burned points and coil problems. You may not need my tach driver, but how's about one of my severe duty "Trash Can" condensers? They not only work great they add a touch of panache' to your distributor.