i just recently purchased a tach dash for my 71 chevelle. i wanted to try out the tach, so i ran a wire from the dash plug out to the distributer. i didnt have the plug for the distributor cap so i just ran a wire with a little post end and connected it to one of the terminals on the disrib. when i cranked the car the tach would only go to about 10000 rpm's. my question is do you have to run two wires off of the distibutor in order for it to work correctly?