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Jaguar Repair/voltage stabilizeer


QUESTION: on input I have 12.5 on out put I have o . I think that is way my temperature + fuel gauge are not working. way no 10 v. on out put.  .v.s. is new, could I have shorted it out?

Mike   Thank u for all your help, I have a wiring diagram , still learning how to use it ,understand it.

ANSWER: Hi Mike, That is true, 12v in and 10v to instruments but it must me connected to the instruments to get a 10v reading. Also the case of the voltage regulator must be grounded.


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QUESTION: I have a g/b wire that runs from fuelto tem. gauge and then t0 output and green wire from battery and oil  and one to fuse, 2 green wires to input and one g/b to output, with one spade left. Do u only use 3 of the 4 spades. Does the screw that holds down the v.s. make the ground?     I am learning slowly , but getting there,  feels good to be learning so much about my car.

Yes, the mount is the ground and the green wires are power wires and the Green w/black tracer wire/s are the 10v output to the gauges. Sometimes Lucas put two green w/black tracer wires in one spade connector and other times they ran two green w/black tracer wires to the 10v output terminals. Thus sometimes both 10v terminals get used and if both green w/black wires are on one wire end, then only one of the 10v terminals gets used.

Even though there are 4 spade terminals there are only 2 connections. Both green power wires and terminals are only one connection. Both 10v spade terminals on the regulator are actually only one connection.

It does not matter if both gauges are connected to one 10v terminal or both 10v terminals.

The method of testing is to use a volt meter and turn on the ignition and test the green wires for 12v+ reading. If you have 12v+ then test the 10v side of the regulator (with all wires connected and the unit mounted in place.) You should see aprox. 10v at the green w/black tracer wires on the regulator. Then test the two gauges at the Green w/black tracer wires and they should read aprox 10v also. To test the ground of the regualtor place the (-) black test lead of the volt meter on the case of the regulator and the the (+) red test lead of the volt meter on the green wire on the regulator and you should read 12v+.

If not, check the black wires with the eyelet end that is on one of the large thumb nuts holding the speedometer or tachometer in place. This is the ground for the gauges.

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.

Associate member SAE EAA member

Import Car magazine

ASE Master Auto with L-1 certification up to 2000

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