I've replaced the original head lamps with halogen?
So after a 20 min drive the left light is dim, plus some power loss on pickup?

Was this a mistake? Can it be rectified?

 

Check the voltage directly at the dim lamp itself (at the lamp holder) , at the fuses, and also at the bright lamp and let me know what the readings are.

This could be a wiring issue, the halogen bulbs if correct should not have this behavior, so there may be more than one thing at play here.

 

I think it's a ground / earth issue. When the car moves, the ground wire moves too and loses partial contact.

 

Interesting Jose, why the ground, the headlights have separate ground wires, so why do you think that the ground would affect one side over the other ? I do know they are grounded in separate places, but these grounds are less likely to be affected by movement.

On that basis dstjohn, check the voltage on both sides of the lamps relative to the battery ground and let us know if it is positive or negative ground. This will tell us which side the fault lies.

If the ground side is reading say 3volts with 12v on the switch side of the bulb, then you only have 9v across the bulb (dim bulb) and the fault lies with the ground somewhere, if you have 0v at the ground, and 9v say on the switch side the fault lies on the switch side.

If you find the dim light issues, hopefully the power loss will also be as a result of the same issue as it came up at the same time, if not we can look at the power loss problem after the lights are sorted.

 

TilleyJon, you answered your question in the first paragraph: separate grounds. So it only happens at the left headlamp, the issue must be at the left headlamp. Curiously this happens in Jaguar cars all the way to 1992 when the Series 3 XJ is replaced by the XJ40.

 

Jose, my question was rather why would you assume it was ground rather than switch line, either could affect the brightness of the bulb, you said you think it's a ground issue, I was just wondering if that was an assumption as the grounds can cause issues, or if you had another reason for thinking it was a ground.

You may well be right, just sounded like you had some extra insight, OP also getting power loss, and I can't think if the left headlight ground is common with any ignition ground, mind you neither is the switch line except when it comes from the fuses.

The ground issues with Jaguar carry on past 1992, part of the fault diagnostics steps for the X-type are to check the grounds, and there are many different ones on that car, they even provided a diagram and which ground points serve which connections !

 

Very Intresting.
Next morning both lights are equal, just as if there was no problem.
I can't see a connection moving and re-setting its self each day.

 

I shall check the voltage at the left & right bulbs.
But there is also a loss in pick-up, I thought this due to the drain on power
supply which the alternator can't keep up?

 

TilleyJon, yes an assumption based on prior experience with my XJ, fortunately not with the S type.

 

I gather this, the dim light is easier to diagnose than the power loss at this point, if it was a power drain, one would expect all the lights to be affected not just one, Jose may well be correct and that there is an earth problem, depending on which earth is causing the problem, it may also be the cause of the power loss, a similar issue can be caused by the supply voltage, there are only 2 fuses in the car, I have not checked the routing yet, but there may be a common supply which is dropping and causing these issues.

Assuming that one issue has caused both symptoms then if you can find the light problem it hopefully solves the power loss issue too.

As I said, if you can check the voltage on both sides of the dim headlight and the good one and let us know if you are positive or negative earth, also is main beam AND dip both affected or just one ? then we can help further.

The headlights come directly from the regulator, the coil and fuel pump are also fed from the same supply but via the ignition switch all of which are un-fused. If you can check the voltage at terminal A3 on the fuse panel and terminal B on the voltage regulator too as these are the common connection points.

Left and right headlamps have separate earths, so do the coil and fuel pump, so there is no common earth, so earth is a definite candidate for the headlight issue, but would not explain the loss of power. There may be 2 issues, so try and sort the headlight issue first.

You could also swap the headlight bulbs over from left to right to just see if the dimming issue moves with the lamp in-case the issue is with the lamp. (Unlikely but could be ruled out)

 

you beat me to it TilleyJon!! I was going to suggest the same thing.

 

Yes, I;ve swamped the bulbs, & it;a a ground fault on the passenger side.



The loss of pickup has vanished,,,for now?


Many thanks,

the two do not seem connected, as I originally thought.

 

Spot on Jose, glad you fixed it dstjohn, the lack of pick up linked with the dim light appeared to be a voltage drop issue, but it would have affected both lights, so glad you have at least one issue sorted.

 

TilleyJon I had a feeling it was a Ground because it is a common issue with the XJ headlights. The question is: where was the fault?

 

The fault lies with the group of connectors on he passenger side{right-hand-drive}. inside wing.
This is original, and very brittle, it;s been suggested to completely, redo,
with trailer-connectors, I'm told it's simple, 8 connectors 4 each side.
The voltage was down on the suspect lamp, but when this very base set-up was moved the lamp returned to normal.


Again many Thanks, David


My friend just bought a 3,8, and said; "it;s like a life-time jig-saw puzzle,
you find one piece and loose another" quote.

 

if the lamp ground is the only issue caused by those connectors, you could run a new wire from the lamp spiraling it over the factory wire harness towards the opposite side of the connector, and then splicing the new wire to the proper wire at the harness. then you test and if the issue is fixed, you cut the old wire at the connector and at the lamp, and if possible, pulling it out completely.

 

Those connections are for main beam, dip beam, sidelight, and indicator if my memory serves me right, and they are the feeds not the ground ?


Corrosion is common, either replace the block and clean up the bullet connectors or replace the lot, you can use a product like Contralube 770 which is a contact grease, and will protect the terminals from oxidization.