Tachometer circuit needed...

[Nigel Goodwin]

how can use this Tachometer for diesel car.thanks for help.

Fairly obviously you need to arrange an engine speed related signal, presumably there's something you could use? - obviously there's no ignition circuit.

 

[ClydeCrashKop]

A couple magnets on the crankshaft pulley and a hall effect sensor will work. Check your alternator for and AUX output which puts out an AC or 12 V square wave signal.

 

[boxer4]

how can use this Tachometer for diesel car.thanks for help.

Diesel engines still have fuel injectors, which could be used to tap a signal from.
(The mechanical diesel injectors from way way back probably could be a problem though )

Else the standby of some crankshaft position sensor can be used to detect when the crankshaft pulls to position. Unless this car is ancient it should already have a computer that needs to know current RPM so there should be something that's already reading RPM. (any specific car we're talking about here?)