Jaguar XK8 Rear Lights Not Working, Check Rear Lights
On the XK8 rear lights that flicker, glow the wrong colour or die usually come down to a melted earth pin in the tail-light plug. CHECK REAR LIGHTS with every lamp lit is the bulb monitoring: wrong number plate bulbs or LEDs, the brake pedal switch, or the module that does the sensing. I'd look at the plugs and the bulbs before buying any part.
How bad is it · Garage, carefully
Fine by day if the brake lights work
A false CHECK REAR LIGHTS message is harmless, but dead stop lights or tail lights make the car unsafe and illegal to drive. Check the brake lights with a helper before you set off.
Which one applies to yours depends on your symptoms, your model year and what has already been done to it.
Likely causes, most common first
Read the check cost before the odds: a free check that rules a cause out beats a likely guess that costs money.
A melted earth pin at the tail-light connector
Each rear cluster earths all its bulbs through one pin in its plug. That pin is too small for the combined current, so it heats, blackens and melts, often on both sides. Once the shared earth is poor, the brake, indicator, reverse and tail circuits feed back through each other.
Rear lights flicker, an indicator glows white instead of amber, bulbs light at the wrong brightness, or the running lights die. BULB FAILURE REAR can come and go with the flashers running fast. It gets worse when you brake or switch the headlights on, and the shift interlock can flicker with the brake lights.
Take off the trim behind the rear cluster, unplug the connector and look at the earth pin and its socket. A brown, black or crusty pin, or melted plastic, is the answer. Also find the black earth lead from the lamp unit to the body inside the boot and make sure it's clean and tight. New bulbs or holders won't help.
Cut the earth wire at the plug and run it, or a new wire, straight to the cluster's earth plate with a larger crimp connector, bypassing the pin. Do both sides; such a repair can last years, with an odd re-tighten of the crimp.
CHECK REAR LIGHTS with every lamp working: wrong number plate bulbs or LEDs
The car measures the current through the rear side lights, brake lights, US side markers and number plate lamps. A bulb with the wrong wattage, or an LED, looks like a fault to the monitoring, so the message appears even though everything lights.
CHECK REAR LIGHTS only once the exterior lights are on, no cruise message, and every rear lamp visibly working.
Lights on, pull the number plate bulbs one at a time and watch the message. Check whether any rear bulbs have been changed to LED or to a different wattage.
Fit correct bulbs. In the plate lamps, for example, swapping wrong-wattage bulbs for 0.5 W LEDs cleared the message on a 2003 XK8; the root cause was not found.
Wing brake lights dead but the high stop light works: the lamp module in the boot
The high-mounted stop light and the two wing stop lights share a relay in the boot fuse box but have separate fuses, and the wing lamps run through a lamp control module in the boot. A failed module kills the wing stop lights and can bring an engine safe-mode warning with it.
High stop light works, both wing stop lights don't, sometimes with an engine safe-mode warning on the dash.
Check the wing stop light fuse in the boot box first. If it's good and a new brake switch changes nothing, the module is next.
Renew the boot-mounted lamp control module.
CHECK REAR LIGHTS with cruise not available: the brake pedal switch
The switch above the brake pedal has two contacts that must agree. It feeds the brake lights, the cruise control and the shift interlock. When one contact is dirty or failing, the car flags the rear lights and switches cruise off.
'Check rear lights' or 'check back light' together with cruise unavailable, while the brake lights themselves work. Or the brake lights only come on with a hard push on the pedal.
Look at the switch and its adjustment under the dash. If a new switch doesn't clear the message, have every module scanned, body processor, ABS, engine and gearbox: the fault may not be stored in the engine module.
Worth trying: clean or renew the switch so both contacts work. The bracket comes off with two small nuts behind a plastic cover near the brake servo, and the switch is easier to fit to the bracket out of the car.
A bulb that won't light in its holder: loose brass contacts
In the rear lamp holders the brass strip to each bulb is held against the galvanised back plate only by pressure. It works loose over time, and the holders don't grip the bulb firmly either.
A new bulb won't light, or one lamp comes and goes, while the fuse is good and the other lamps work. Often after the car has stood.
Pull the holder and look at the contacts and where the brass meets the back plate. Any bulb of the right type will do; it doesn't need to be a Jaguar one.
Worth trying: clean the contacts with a pencil eraser, and wedge a short piece of thin solid wire, with a drop of glue, between the brass and the back plate until it's tight.
CHECK REAR LIGHTS that stays after all of the above: the bulb sensing in the security module
The rear bulb check runs through the security and locking module, which holds a sensing resistor for each monitored circuit. A burnt resistor or a cracked solder joint there raises the message with sound bulbs.
The message persists with correct bulbs, clean contacts and a good brake switch.
Don't swap the module on a guess. Unplug it and measure the resistance of each rear lamp circuit from its connector, comparing with the bulb on its own, using the wiring diagram for the pins.
Worth trying: have the module repaired by a specialist; on one 2005 XK8 that cleared the warning after new switch microswitches had not.
The order to check them in
The point of the order is money: each step either rules a cause out or makes the next one worth doing. Green is free, amber costs a little, red is the one to arrive at last.
Note exactly what's dark
Which rear lamps, and whether it changes with the brake pedal, the headlights or an indicator. Note whether cruise control drops out with the message.
freeBulbs and holders
Check nobody has fitted LEDs or the wrong wattage, especially in the number plate lamps. Clean the holder contacts and make sure the brass strips sit tight.
freeRear cluster connectors and earth
Remove the trim behind each rear cluster and inspect the earth pin in the plug, then the lamp's earth lead to the body in the boot. A burnt pin explains flicker, wrong colours and dead running lights.
freeFuses and the brake switch
Check the lighting fuses in the boot box, then the brake pedal switch if the message comes with cruise unavailable or the brake lights need a hard push.
a fuse or a switchModules last
Only then the lamp control module in the boot or the bulb sensing in the security module, after a scan of all modules.
a module or its repairThe fuses named above — where they sit
The highlighted position is the one the procedure talks about. Pulling a fuse is a stop-gap, never a repair: check what the circuit feeds before you pull it.
Circuit descriptions from the Jaguar fuse tables, 1997 edition. Drawing by jagaux.com from the factory electrical guide. Fuse layouts change between model years — read the legend on the lid of your own box before pulling anything.
What it usually isn't
Don't spend money here first:
If none of this finds it:
On jagaux.com
- Jaguar XK8 Headlights Not WorkingIf the headlights or front side lights are the problem rather than the rear.
- Jaguar XK8 Engine Failsafe ModeIf an engine failsafe warning comes up together with the brake light trouble.
- Jaguar XK8 Key Fob Not Working, Alarm or ImmobiliserIf the locking and alarm misbehave too, as the same security module watches the rear bulbs.
- XK8 fuse boxes, including the boot boxFind the lighting fuses and relays in the boot box, drawn.
- Jaguar XK8 Stuck in Park, Gear Shift Won't MoveIf the gear lever is also stuck in Park — the same brake switch drives the interlock.
- Jaguar VIN decoderConfirm your exact model year, engine and factory options before ordering parts — free.
Ratings, fuse numbers and torque figures vary by model year and market. Read the legend on your own car before pulling anything, and use the figures in the manual for your car, not the ones in a video.
Check your VIN: exactly which car you have and which bulletins apply to it.