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Jaguar Repair/tacho generator


QUESTION: how do i check tacho generator is giving out a voltage using standard multimeter on jag xk150

ANSWER: Hi Dave,

It has been many years cince I worked on a 150 and I didn't even remember the 150 haveing an electric tach but I would guess it is the same unit used on the E-Type and we used a multi meter and as I remember the tach generator produces AC. So put your meter on a low AC scale the run the engine. If it were DC it could only produce pulsing DC current as there is no rectifier or regulator. You can't harm it either way by putting you meter on a low volt scale on AC then check on a low scale for DC if you don't get a good reading.

It must be AC because my E-type wiring diagram shows both wires the same color and no marking of Pos and Neg. If it were DC it would have to be connected up according to the polarity and it is not.


---------- FOLLOW-UP ----------

QUESTION: Do i put the multimeter across both spades on the generator, or on each spade seperately and to earth. Thanks

Hi Dave,

Put the volt meter on a low AC volt scale if it is not an automatic range volt meter. Put the test leads across the two pins on the tach generator with the car's wires removed and run the engine to see if it puts out a small voltage. If it does not produce any voltage at all remove the three bolts secquring it to the rear of the head at the intake came and look at the "Dog" (rubber covered piece that connects the cam to the generator) They can get damaged with age.

If the generator does produce voltage ( I don't remember the amount of voltage) then test the two wires that go to the tach and test the green power wire on the tach that should have 12v on it with the key "ON". Also test the tach case to see that it is grouded. If all of that is good, then it is the tach itself that is bad. I believe "Nisonger" still repairs electric tachs.
Try,  Also they may be able to tell you what voltage you should see on the volt meter.

Let me know,


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Howard M. Fitzcharles III


Jaguar from the XK 120 to XJ-6 ser. 3 1987


Dealership line mechanic on MG, Triumph, Jaguar for 15 years, Instructor in commercial mechanics school 2 yr. Product information manager for piston and valve manufacture, Instructor & hotline answer man for import car parts importer 15 yrs.

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