Cummins tach question

[conchy joe]

Ok so I feel really stupid. On a Cummins 4BT or 6BT, where does the tachs get their signal from on the motor? The alternator?

If so I have a Motorola alternator and cant find a
part number or a wiring diagram for the alternator.

[Harry Babb]

Joe
The tach on my 6B's gets its signal from the Alternator......and I have no idea of the brand of the alternator......I will look next time I open the hatch.

I am not going to do it quite yet but you can install a Pickup in the flywheel housing that counts the teeth on the ring gear and sends impulses to a tach......but I think (I'm not sure) you have to get different tachs....

I've heard some of the guys complain that the Alternator Tachs are not accruate.

Beyond that "I don't know nuttin bout no Motorola alternator Ms Daisy"

hb

[wmachovina]

The Tachs on my 6bs come off of a flywheel sensor. My tachs came from aetna and are +- 1 rpm. Very accurate.

[conchy joe]

I appreciate the info. I have confirmed the signal comes from the alternator however all the wiring diagrams I can find don't show a motorola alternator, so I am now asking does anyone know which wires go to which terminal on the alternator? The only one I can discern for sure is the positive??

BTW i have new original harnesses going to original new VDO guages

As always thank you guys.

[Harry Babb]

Joe
The tach wire is Gray.

Don't know about the terminal on a Motorola Alternator.

Is it labeled in some way on the back of the alternator ?


hb

[In Memory of Vicroy]

The output terminal on the alternator marked "AC" puts out alternating current that the tach reads and converts the cycles into rpms. Tere is a chart for each alternator (since the pulley size affects the frequency of the output) My alternator pickups drove me nuts so I converted to magnetic flywheel pickups - VDO gave me all new parts free at the FLL Boat Show to do the job. Hint: the Cummins 6B flywheels have 159 teeth.

Convert if you can. Much better system.

UV