2″ 52mm Water Temp Gauge Fahrenheit F with Sender Kit Digital Blue LED for 12V Car AUTO

Throw away the limited instructions that come with this tach, On the back, you will see what looks like (and is labeled like) a toggle switch. It’s not. It’s an intermittent switch to use to change the cylinder count which I will explain in a second.First, connect the tach to 12v power, Once connected, it’s going to most likely default to a 1cyl engine. Using the intermittent switch on the back, hit it once and you should see a “1” displayed showing the current setting, then tap it again for a “2” and again for a “3” until you see the number that corresponds to the number of cylinders your engine has. Once you connect the signal wire (and assuming it’s transmitting 1 pulse per cylinder) the correct RPM should be displayed.As others have mentioned, there is a fair amount of delay as it only updates maybe 1x or 2x per second. If you need something more accurate, you’ll wind up spending a LOT more money. However, if you are simply looking to see what RPM your idle is at, your RPM at cruising speed, etc, this will work well.