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Jaguar Repair/voltage stabilizer


QUESTION: put in the v.s. today and all is working well. I mentioned I was have trouble will the oil gauge.It goes to 6olb. and never comesback down. Can u give be a idea on what to look for.
 Thank U for all the help u have giving me. I have learned so much. I feels really good, to have done this, what a great site to have, and what GOOD people to be willing to help people like myself . Thank u again ,and all the people at allexpert for there help.

ANSWER: Hi Mike,

Most of these gauges are frail inside so it don't take much to make the needles stick and not return and the same is for them starting up too. If when you start up, it is slow to respond try tapping on the gauge first. Or if it don't return to zero when shutting down try tapping on the gauge with your finger.

The electric gauge has a large sending unit on the right side of the block down low either on the block or on the filter block which can cause a problem too. There are two sending units a large one and a small one. The larger one is the gauge and the smaller one is for an idiot light.

If tapping on the gauge after shut down does not make the needle return to zero try removing one of the wires from the gauge to see if that makes it return. If removing a wire makes it return and the ignition is turned off then you need to test the green wire on the gauge for power with the key off. There should not be any power on the green wire with the key off.


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

QUESTION: I sorry ,I am not sure I understand the answer. When I turn on the car the needle on theoil gauge goes right to 60lb., before I started the work , it would go to 60lb., them after a few minutes drop down to about 30, to 40 lbs.  Now it just stays at 6olb. I have tapped the gauge and nothing. When I turn off the car the needle on the oil gauge,drops down to 20lb. Please advise.  Thank u for all your help

Symptoms of any electrical problem are almost completely useless for diagnosing the problem. The ONLY way to find the fault is by testing.

There are only two wires on the gauge. (except a light bulb wire) There is a plain green wire that is the power wire to the gauge.

The green wire must have 12 volts to it with the key "ON". And it must have ZERO volts on it with the key "OFF". This can be tested with a volt meter or a 12 volt test light.

The other wire is White w/brown tracer wire. This wire goes to the sending unit on the engine.
The sending unit grounds this White w/brown tracer wire by how much oil pressure is applied to the sending unit. Without any expensive test equipment you can't test the sending unit. But there is a test for the gauge.

To do the test you need a 12 volt test light. (not expensive)

First remove the White w/brown tracer wire from the gauge. Now turn the key to "ON" (not start). connect the clip of the test light to a good ground. Now, touch the point of the test light to the Green wire. It should light your test light brightly. The gauge should be reading Zero at this time. Now touch the post on the gauge that the White w/brown tracer wire came off of with the point of the test light while watching the gauge. The needle should deflect all the way in one direction and when you remove the test light point the needle should go in the opposit direction all the way. (Don't leave the test light point on the poat for a long time, only touch it with the point of the test light to see what the gauge does.

This does not test the accuarcy of the gauge it is only a rough test to see if the gauge responds to a ground.

If the gauge don't respond as above it is bad. That don't mean the sending unit is good, it just shows the gauge is working or not working but not it's accuaracy.

I worked in several Jaguar dealerships and none of them had the test equipment to test gauges and sending units. We used the procedure I listed above to see if the gauge operated and if it didn't we put in a new gauge and then if it still didn't work we replaced the sending unit also. Most of the time only one or the other were bad. It was rare to find both bad.

The reason that the sending unit is so difficult to test is because it operates like a voltage regulator which means it is opening and closing the circuit all the time.

Let me know the results of the tests.


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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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