Tachometer connection.

[KANTANKRUS]

Clueless, thats why I am asking.

 

How does a tachometer read the RPMs of a motor?

 

Do our trucks have a cable to attach too something? (If so) What?

 

My 87, 4x4, AX15, 4.0 liter, does not have a tachometer within its instrument cluster.

[eaglescout526]

From my understanding from the FSM, the tach reads pulses sent from the coil from when it fires. 

[KANTANKRUS]

59 minutes ago, eaglescout526 said:

From my understanding from the FSM, the tach reads pulses sent from the coil from when it fires. 

What is the FSM?

[eaglescout526]

Factory Service Manual. 

[scaleless]

9 minutes ago, RestoringNV said:

What is the FSM?

 

Factory service manual.

The ICM generates a PWM signal which is filtered to a constant voltage by the tachometer.  The signal gets to the guage cluster regardless of if it has a tach or not.  The tach is pulled towards zero by a permanent magnet, and the voltage from the ICM energizes an electromagnet that pulls the needle away from zero.  The balance between the permanent magnet and the electromagnet is what controls the needle position.