Motorola tachometer

[TOW'D]

Howdy Gang,
 A friend has a converted 40ft F/G fishing boat with a huge Skanda(spelling? built by the SAAB people)diesel.
The electronic Motorola tach just stopped working- there is a sensor threaded into the bell housing to read the rpm.
 Both the tach and sensor have continuity( no open circuit), the wires are good-power and ground to tach head is also good.
So the only thing I can think of being wrong is maybe the magnet came out of the flywheel.
Now I really don't know if there is a magnet in the flywheel or if the sensor reads the flywheel teeth.

Anybody have any suggestions
thanks
hank

[Patrick]

Had a setup like this in a big truck I used to have. It doesn't work off the teeth, that's for sure! Never had a problem other than a bad connection . Not sure how it read, suspect a magnet.

[TOW'D]

Thanks Patrick
I'm going to test the sensor with a magnet by shaking it back and forth to see if the needle will move.
Then spin the flywheel (by hand)and look at the teeth for a missing magnet
At least there is a lot of space in the engine room to get around.
cheers
hank

[Zulfiqar]

if its built by SAAB they must be using a corbino effect wheel on the crank to trigger a hall sensor, thats how SAAB usually like it    check the resistance of the sensor itself - that may cause a dead signal

[TOW'D]

We tested the sensor by moving a magnet across the face and got no reading
the gauge needle does move when the key is turned on so it must be good

Having a hard time finding the parts
thanks for the reply
hank