Dash Lights not working/Light switch stalk fix

[kingzetts]

I had not noticed this when I bought my XK8 recently but the dash lighting was not working at all. Research on some other XK8 forums on the web and some on-vehicle testing led to a diagnosis of a failure inside the light switch on the left-hand stalk. A very helpful conversation with the experts at XJK Garage Services confirmed this was the likely problem.

In the hope it may help others, here's a description of the symptoms, the troubleshooting, and the fix.

Symptoms: when the ignition was first turned on the dash lighting (main instrument pack, secondary 3-dial pack) came on briefly, then went out, whatever the position of the light switch.

With the light switch on sides, the dash lighting worked but the side lights/number plate lamps did not work.

With the light switch on heads or auto, the sidelights and headlights worked normally but the dash lighting went out totally and the switch backlighting was also not working.

The dimmer switch did not have any effect in any position including past the over-ride detent. The lights were either on full (sides position) or not at all (heads/auto).

Diagnosis/troubleshooting: armed with the wiring diagram, there is a red/white wire which connects to the dimmer module and the body processor module and which is grounded via the lighting stalk when the light switch is in any position except off. This same wire is also connected to the dimmer switch. There is a blue/yellow wire connected to the body processor module which is grounded through the light stalk when the light switch is on heads or auto.

By removing the steering column lower shroud (2 screws below the shroud) access can be gained to the dimmer switch. By carefully grounding the terminal to which the red/white wire connects, it was established that this caused the dash lights to illuminate in all switch positions and indicated that the light switch was malfunctioning.

This explained the fault symptoms as follows; by not grounding the red/white wire the dimmer module is being told that the lights are off, so it does not power up its power outlets to the dash illumination. At the same time the body processor module is also being told the lights are off, so it fails to switch the sidelights on but it does switch the dash lighting on which is the normal daytime state. When the light switch goes to heads or auto, the BPM is grounded via the blue/yellow wire and correctly lights up the sidelights and headlights, but it also powers down its supply to the dash lights allowing the dimmer module to take control - which it cannot do because it is not getting the ground signal from the red/white wire.

The fix: simply replace the indicator/light switch stalk. I obtained a good used unit via XJK for £90 delivered, around half the price of a new unit from Jaguar. I could have sourced cheaper via eBay but wanted the confidence of being able tosend it back if it was dud.

To change, I removed the airbag (2 torx screws from behind the wheel), steering wheel, lower column shroud (2 screws), upper column shroud (3 screws), stalk (2 torx screws accessible once the shroud and wheel are off). It is also necessary to remove the lower dash panel (2 bolts) in order to get access to all the wiring connectors. This is all very straightforward and took around an hour from start to finish.

My dash lights now work as intended.

[JimboV8]

Hi John,
I would like to thank you for taking the time in not only posting a problem but also the diagnostics you carried out leading to a succesful fix. This kind of detailed information is invaluable to those of us who enjoy tinkering and in the long run, helps to save some pennies.

Thanks and kind regards,

Jim.

[mike020150]

An excellent, highly detailed posting about this problem. Just one comment for those not conversant with airbags; please follow all the safety advice when working on them. They do contain explosives and caustic soda! The battery must be disconnected for a short period of time before attempting to remove it (go and have a cup of tea to be sure). Wear eye protection in case of accidental deployment and similarly, always hold the airbag unit away from your body. Mike.

[Nik]

Thanks for a great write up John

All the best

Nik