Tachometer: Tachometer installation is relatively simple but also two normal light linetwo needleusually red wire to positive and black wire to negative.But the only difference is that there are signal lines to find the local connection. Where the signal line can be connected to it there are three general connection of the car: 1. Can be accessed by the ignition coil negative (negative ignition coil wire)tachometer is based on the principle of magnetic workhe can receive the very beginning of the ignition coil current thrust generated when a pulse signaland this signal is converted to turn the displayed value.The larger the number of revolutions of the engine the more pulses are generated transfer values ​​shown in the table will be bigger. 2. Can be accessed on the crankshaft position sensor signal line. Vehicle models with different structures on the crankshaft sensor is used in different. Separable magnetic pulse photoelectric Halls of three type. He usually mounted on the front end of the crankshaft camshaft front flywheel within appliances or points.Two lines is generally magnetic pulse and photoelectric signal line connected to try to clear.Three lines on the Hall -stylea supply line mostly red -5Va black line negativeand the other one is the signal line.(There are four lines with the exclusion of the other part of the car interference.) 3. Most cars now have a collection of automotive engine rpm signal can check the ECU circuit diagram of the original car computermake sure your original car from which the number of revolutions signal pin out then the signal line connected to its output on OK.