Why You Need A Tachometer And How To Install It

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Your guide to the perfect shift.

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Why Do You Need a Tachometer?

Almost all modern cars include a tachometer, so it must be important right? Some feel that this is not always the case. If you drive an auto and only care about getting from point A to point B, then this device will have little impact on your life, save to possibly identify what gear you're in - if you're interested. However, if you prefer a hands-on approach and love the thrill of driving at higher speed, a tachometer is much more significant.

A tachometer monitors engine crankshaft revolutions; rather than telling you how fast you are going, it lets you know how many rotations per minute are occurring within the motor itself. In days gone by, we used a tacho to tell us when the right time is to shift gears, assuming you were driving a stick shift. However, some older cars may not have been fitted with one, resulting in owners installing a tachometer themselves. Fortunately, most new cars come equipped with one, although the usefulness of said rev counter is still up in the air if you drive an automatic.

Tachometer unsplash.com
Tachometer on a Diesel Car unsplash.com

How Does a Tachometer Actually Work?

How a tachometer works is rather simple. Once your engine is activated, the fuel is ignited, which causes the pistons to rotate the crankshaft of the motor. This is usually where the device is installed. The working principle of a tachometer is that it monitors these movements and generates an electric impulse, which is then transmitted to the display. Depending on different types of tachometers, this is shown as an analog movement of the needle, or a digital representation. The exact function of each depends on its design, but the end result is the same - it displays how many times the crankshaft turns, with higher revolutions per minute (RPM) meaning your engine is working harder and generating more speed. The term red-line refers to when the needle of the rev counter hits the highest RPM count (literally indicated in red on the tachometer), although pushing the engine to this point for extended periods of time generates friction and heat, and can cause damage. In this regard, having a tachometer can be useful. That is, if the sound of the engine straining is not already a dead giveaway.

The Different Types of Tachometer Design

Automobile tachometers generally come in one of three styles.

  • Mechanical tachometer - The earliest iteration of these devices were quite simple. A drive cable runs from the camshaft or crankshaft to the tachometer mechanism. The slide near the shaft picks up the torque from the engine and transmits it to the tachometer. This causes the magnetic mechanist to move the needle accordingly. However, since the cable twists during the transfer of force, the reading may not be entirely accurate.
  • Analog tachometer - A slightly more advanced version, the analog version functions on the same principle as the mechanical. But, instead of using a cable, it relies on an electronic transmitter attached to the crankshaft. This relays information to the magnetic coil inside the tachometer, which moves the needle to show the revolutions per minute. Much like the mechanical option, it has a margin of error of around 500 rpm.
  • Digital tachometer - The most recent model of the device, the digital tachometer doesn't rely on a magnetic coil like its predecessors. Instead, it uses a microprocessor to pick up the signals from the crankshaft sensor. These are then translated into a definitive value, which is displayed on the tachometer gauge. The margin of error here is usually as small as 100 rpm.
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Mechanical Tachometer Pexels.com
Analog Tachometer unsplash.com

Can I Install a Tachometer Myself?

If you have an older vehicle that, for some reason, doesn't have a tachometer, you could consider installing one yourself. Hooking up a tachometer is not so complicated that you need to employ a mechanic. A DIY job works just as well, so long as you have a step-by-step guide. If you are adding an additional tachometer or installing it in a car that doesn't include one as standard, you may have to mount it on the dashboard. You will also need a few tools and parts to get the job done properly.


  • The actual tachometer - this is relatively cheap, available for as little as $33.
  • Wire cutters and strippers
  • A drill and screwdriver
  • Ratchet and sockets
  • An automotive diagnostic tool
Remote Tachometer Pexels.com


Do you need a tachometer?

While useful, the meter is not actually essential to vehicle functions. This is especially true in the case of cars with an automatic transmission. However, it does help to determine the best gear shift intervals on a manual vehicle and it may help to pick up problems when your auto is shifting inefficiently.

Why does my tachometer not work?

Generally, this is the result of a blown fuse or poor wiring. In the case of a digital tachometer, the problem may lie with the display itself. If your diagnostic check of the tachometer fuses and display don't turn up any results, you may have to contact an auto-electrician. However, failure of a mechanical tachometer can only indicate one thing - a faulty cable that needs to be replaced.

Where does the tachometer connect?

From the gauge, the tachometer will connect to either the ignition system or an electronic device that monitors all the engine functions. Naturally, it also includes a wire for power and one for grounding.

How do you test a tachometer with a multimeter?

If you need to check whether your tachometer is working correctly, you can use a multimeter. Simply set it to AC voltage and connect the negative clamp to the chassis to ground it, while the positive lead will connect to the tachometer wire. Start the vehicle and allow it to idle while the meter displays the voltage.

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