How to connect the tachometer to the car

How do I connect the tachometer?

The tachometer measures the revolutions of the engine. Its readings are not less important than the speedometer readings: the instrument scale of the analog construction has green, yellow and red sectors corresponding to the ranges of the engine RPM. Often “fly out” in the “red zone” of the readings is not allowed: overheating and engine wear are significantly accelerated.

Connection to a gasoline engine

The tachometer is connected to the alternator, which communicates with the engine shaft. The fact is that, whether it is a full-fledged car, scooter or motorcycle, the readings are taken mainly by the alternating voltage, which is produced by a three-phase generator. The simplest tachometer on older cars is a voltmeter made from a microammeter with the addition of one diode and one high resistance resistor. Electronic devices, including Chinese ones, have a slightly more complicated structure: they have an analog-digital converter – like universal digital multitesters.

The task of the tachometer as such is to tell when the driver should manually shift gears.

In cars with automatic transmission, there is no need to shift manually: the “robotized” or variator circuit will do it itself. But this does not mean that there is no tachometer in the electric circuit of the car – it interacts with the electronic control unit (ECU) of the engine. The tachometer also adjusts the operation of the car at idle – before the driver sets off.

Before you connect the tachometer built into the new dashboard, get a remote one. The second will help to adjust the work of the first clearly, with the highest accuracy. The easiest option is to buy the same dashboard you had before. To remove the old dashboard – and connect the new one, the car’s torpedo will have to be disassembled. Before repairing, remove the minus terminal from the battery. Clearly follow the wiring diagram. Remote tachometers can be connected from the cigarette lighter – they are most convenient.

Connect the remote tachometer on as short a cord as possible to reduce reading errors.

For the remote tachometer to read RPM as accurately as possible, connect it to the ignition coil. Remove the protection from the steering wheel – and take out a few wires, highlight the ones that fit the coil. Observe the color coding when connecting the remote gauge.

On VAZ cars equipped with a non-contact ignition system, the tachometer is not connected to the coil, but to the commutator. For typical models of the tachometer “TX-193” white cable is used to bring voltage to the backlight, the red wire – to the ignition switch through a fuse. The white wire with black marks is connected to the “ground”, brown – to the terminal “K+” on the coil. The black wire is to the charge current indicator relay, installed on the right side from the engine. The gray-black one is to the engine oil pressure regulator: it is located on the left side of the engine.

In particular, on VAZ-2019 cars, “plus” and “signal” wires are connected to pins “B” and “K” on the ignition coil. The third one, the minus one, is in a convenient place to the car body.

The VAZ-2110 has a tachometer with 4 pins. On cars with injection it is connected to the ECU via an additional lead. Measurements are made by the signal location of the crankshaft.

Finally, in more modern cars, produced already in the 2010s, the tachometer is not without interaction with the ECU. On injector cars, the tachometer is connected minus to “mass”, “plus” – to the positive terminal from the ignition system. The first input is connected to the ECU, the second – to the crankshaft position sensor.

To connect the tachometer on a car with gasoline engine, follow the following diagram.

Connect the black wire to the “minus” of the power supply.

Red wire – connect to the “plus” controlled by the ignition switch.

Connect the third wire (color not shown strictly) to the trambler interrupting block (if the system is contact). In a non-contact system, it is connected to the switched voltage supply block.

If there is a backlight in the instrument, connect it to the wire that supplies power from the battery, through the same ignition lock. The lock itself in more modern cars may be equipped with an additional output.

Tachometer connection scheme on KamAZ is similar to that of VAZ. The connection sequence is determined only by the fuel on which this machine is driven. All older generations of KamAZ run mostly on diesel fuel, not gasoline.

Diagram of connection to the diesel engine

In cars with diesel engines, the tachometer reacts to impulses sent by a special terminal. To successfully connect the device, remove the protection on the generator. To figure out how to install and connect the tachometer to a diesel engine vehicle yourself, do the following.

Locate the pin with the marker “W” on the alternator, this is where the tachometer output is connected.

Short-circuit the contact coming from the oil booster. If there is no such short circuit, the instrument will give unreliable readings.

If it is not possible to connect to the pin with a “W” marker, it will be necessary to disassemble the alternator itself. Connect the wire between the winding and the three-phase diode bridge to the tachometer cable.

Insulate all terminals , and reassemble the alternator as it was assembled by the factory.

If you don’t know how the tachometer and the diesel engine work, you can’t connect the unit correctly: in this case, get help from the service center.

Checking the operability

Having connected the tachometer to the car instead of the old one, make sure that the device reacts to the change of the engine rpm at idle. If the measuring head (pointer device) turned out to be defective, you will probably not be able to restore it: the coil of electromagnet uses too thin (thinner than a human hair) winding wire, which is extremely difficult to obtain, and it would require “jewelry” sensitivity for such fine motor motions. It makes sense to restore an old device with a surviving meter head if you can find parts of the same rating. A digital meter, on the other hand, is often not rebuildable if the microcontroller or digital LCD scale is broken.

Once the tachometer is mounted, accelerate with varying degrees of intensity. The engine speed at idle of the machine is considered sufficient at a value of 1000 per minute.

The tachometer of the arrow type is adjusted by the angle of deflection of the arrow. If this angle is too small, a capacitor with a capacity of about 1 microfarad is inserted between the signal lead and the plus. If the tachometer is off-scale, a variable resistor of up to 1 kiloohm is placed on the signal lead – and its exact value is set so that the device stops “lying”.

If the first stage of tachometer adjustment for reliability of indications has passed successfully, the car is given a running load. The motor should be accelerated to the readings of the device, so that the engine speed was not too high. If this is not the case, the tachometer must be readjusted.

Before putting everything back together as it was, check if the wires are securely insulated and there is good contact on the terminals of the cables and functional units.

Try driving around, shifting speeds. If you have a car with an automatic transmission, it does all the shifting work by itself. Accurate shifting is sometimes impossible without monitoring the digital tachometer.

On older cars equipped with “manual” instead of automatic transmission, the operation of the car (and driving on it) without tachometer indications is possible: an experienced driver by ear will determine when it’s time to shift to a higher gear. But such estimation is purely subjective. Conclusion: it is difficult to do without a tachometer, and even on a usual “mechanics” it should be always operable and functional.

How to connect the tachometer to the car

Tachometer – not at all an obligatory element of the car, but at the same time very useful. The device significantly prolongs the life of the engine and saves you from expensive repairs. Everyone who cares about his car should know how to connect the tachometer. This is what we will talk about.

What is this device

To begin with, you need to understand what the device is and what its main functions are. Tachometer is a measuring device that determines the speed of the crankshaft of the engine. The unit of measurement is revolutions per minute (rpm). Almost every modern car is equipped with a device, as it helps to use competently the possibilities of the engine. If the basic configuration tachometer is not provided, you can buy it separately and install it on both the diesel and gasoline engine.

Main function of the device

The purpose of the device in the car is to select the most appropriate gear for continuous operation of the engine. Most of the modern car brands are equipped with analog tachometers. The car owner is aware of the need to change gear with the help of the arrow, which is rapidly creeping to the critical mark. There are several types of devices, but their principle of operation is similar.

How the device works

According to the principle of operation, tachometers are divided into magnetic and electric.

How magnetic models work

Magnetic tachometers work based on the induction of eddy currents. These are produced when a metal disk is placed in a rotating magnetic field. The currents and the magnetic field begin to interact with each other, causing the non-magnetic disk to rotate. The tachometer hand is connected to this disk. It has a return spring on its shaft, and the magnet is connected to the crankshaft by a flexible shaft. Increasing motor speed makes the magnet move faster, deflecting the non-magnetic disc. This whole process is demonstrated by the arrow.

How electric models work

Such tachometers measure electrical signals and pulses. The ignition system and the generator of the gasoline engine generate electrical signals according to the crankshaft speed. Thus, the desired signal comes from the electronic control unit.

Read also: What is the crankcase, why does the engine need it and what materials is it made of

Types of devices

Tachometers are divided according to the method of information output and the method of connection. In the first case, there are two types of devices:

• Digital (the data is displayed on a small screen);
• Analog (the driver receives information with the moving arrow).

According to the principle of connection tachometers are:

• Regular. These models are equipped with modern car brands. They are built into the dashboard.
• External. Often such devices serve as a replacement for missing regular tachometers. Their main advantage is that they well control revolutions at idle and have a smaller error rate.

Connection to a gasoline engine

Now we will tell you how to connect a remote tachometer. To properly install the device, you will need a connection diagram of the purchased tachometer, which is included with the device. If there is no instruction in the kit, then the installation will not be difficult for you. You do the following:

1. Fix the device in a convenient place for you. The best place is on the dashboard or its surface.
2. You get to the wires from the tachometer. There should be three of them: black, red and one other wire of any other color depending on the model of the device.
3. The black wire connects to the body of the car.
4. The red wire is connected to the terminal of the ignition switch, which transmits 12-volt voltage when the ignition system is activated.
5. The last wire is connected according to the ignition circuit (contact or contactless). In the contact circuit, the wire is connected to the trambler chopper, in the non-contact version to the voltage switch.
6. Many tachometers have a backlit dial or display. If it is provided in the technical specifications, connect the device to the car’s parking lights with the appropriate terminal on the ignition switch.

Connection to the diesel engine

Let’s consider how to connect an electronic tachometer to a diesel engine. Installing the tachometer is simple enough.

1. First, you need an overpass or an inspection pit in order to remove the protection from the alternator and clean it.
2. You will find the terminals on the coil responsible for various processes. You need the terminal labeled “W”.

Note: if you don’t find the right terminal, use the pinout to the alternator rectifier on the coil. Select any one of the three terminals and solder it to the end of the instrument cable. Insulate the connection.

1. Connect the contact from the tachometer to it.
2. Close the contact of the oil pump. This is necessary for more accurate measurement, because otherwise when 2500 rpm is reached, the oil pressure light on the dashboard will turn on.
3. Check that the electronic tachometer is correctly connected and put the alternator cover back on.

Important: check that the wires are not in contact with moving parts.

Checking the operation of the unit

After connecting the tachometer to the engine, be sure to check that it works. If the arrow moves, everything is connected correctly. But do not forget that the device can fail (the arrow begins to “jump”, etc.) for some reasons. The most common causes of breakdowns are:

• Prolonged operation of the motor, causing vibration and damage to the display;
• Insulation disorders, disconnection of contacts and their oxidation.

You can identify and solve these problems on your own. If the cause is in the sensor itself, which is out of order, then it will be necessary to replace it. In complex cases, the right solution will be a trip to the service station.

To summarize, let us note that the installation of the tachometer is not such a difficult task. But you should not take up the case without the necessary theoretical and practical skills in car repair. If you are not confident in your abilities, it is better to turn to the experts. Share your opinion in comments!