Jaguar XJ6 (X300) Brake Lights, Tail Lights Not Working
When the brake, reversing and rear fog lamps die together on these cars, it's usually one fuse in the heelboard box under the rear seat that feeds the rear lamp module — and it often blows while the high-level stop lamp bulb is being changed. One side's tail lamps out is that side's fuse. I'd test the fuses live before looking at bulbs or modules.
How bad is it · Garage, carefully
Don't drive without brake lights — fix it first
Without brake lamps the car behind gets no warning. With every brake lamp dead the selector can also stay locked in Park, because the interlock needs the brake lamp circuit.
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.
The fuse feeding the rear lamp module, under the rear seat
The rear lamp module takes one of its feeds through a 10 A fuse in the right-hand heelboard box under the rear seat, easily overlooked because it's out of sight. A slip while changing the high-level stop lamp bulb, or an LED bulb fitted there, blows it.
Brake, reversing and rear fog lamps all die at once, just after work on the high-level stop lamp; tail lamps and indicators still work, and the dash shows no warning.
Lift the rear seat cushion and test every fuse in the right-hand heelboard box with a test lamp — a fuse can look whole and still be open.
Replace the blown 10 A fuse. If it blows again, look for a pinched wire at the high-level stop lamp.
One side's tail lamps out: that side's fuse
The tail and side lamps on each side run from their own fuse. If one side's tail lamps are out but its brake lamps still work, the fuse is the first suspect, not the lamp module.
Both tail lamps on one side dark while the brake filament in the same bulb still lights; the bulb warning may not even come on.
Find the tail lamp fuse for that side — the numbers are in the fuse block below — and test it live.
Replace or reseat the fuse.
The high-level stop lamp: loose, or its wiring broken
The third stop lamp on the rear shelf comes unstuck, and its loom — on some cars under the parcel shelf rather than in the boot — breaks where it flexes. A lamp hanging loose is also how its wires get pulled apart.
The high-level lamp dark, loose or fallen off, the other brake lamps fine.
Look at the lamp and follow its wires under the shelf for breaks.
Bond the lamp back with a strong adhesive such as epoxy. Rejoin broken wires by soldering, cover each joint with heat-shrink and leave some slack for movement.
A failed bulb, or a bulb of the wrong rating
There are four brake lamps, so one out is easy to miss, and each rear cluster carries two bulbs per circuit. The bulb-failure system measures current, so a bulb of the wrong wattage, or a mismatched pair, sets the warning too.
The bulb warning comes on when you press the brake, or with the lights on, though no bulb looks dead.
Get someone to press the pedal with the engine running, or look at the reflection in a window. Check the upper lamp on the shelf and both bulbs in each cluster, and match the wattage — 21/5 W for the tail and stop bulbs.
Replace the dead bulb and fit correct, matched pairs.
On 1995 cars, the stop lamp fuses and relay in the boot
On 1995 cars the stop lamps also run through 15 A fuses in the boot fuse box, one per side. The high-level stop lamp has its own relay there, on a red base.
Brake lamps dead on one side only, or only the high-level lamp dead.
Test the boot box fuses with a continuity tester rather than by eye, and swap the red-based relay for a known good one.
Worth trying: replace the fuse or relay, and clean the relay contacts.
Later XJ8 rear lamps fitted: a permanent bulb warning
XJ8 rear lamps bolt straight on, but the X300 has an extra tail bulb on each side where the XJ8 has a reflector. With that bulb missing, the module sees a failed lamp and the warning stays on with the side lights.
Bulb warning on whenever the side lamps are on, on a car with the later, smoother rear lamps.
Look behind the rear lamps for an empty bulb position or a holder that doesn't fit.
Drill the reflector cavity for the extra bulb, use the X300 holder and wire it to the side-lamp feed. Bridging the empty contacts silences the warning but puts heat into the lamp module.
All brake lamps dead and the selector stuck in Park
The shift interlock only releases when it sees current through the brake lamp circuit. One working brake bulb is enough; none, and the lever stays in Park.
Engine starts, but the lever won't leave Park and no brake lamp lights.
Put a test bulb in near the brake switch to prove the feed from front to rear, check the earths at both rear lamps, and test every fuse. Only then suspect the body processor.
Worth trying: restore one working brake lamp circuit first; the lever follows.
The rear lamp module itself
The rear lamp module has sense resistors and coils on its board for each lamp. A short in the lamp wiring, or a faulty plate lamp, can scorch them, and then lamps on one or both sides stay dark.
Lamps dead after a short or after relays were pulled, fuses good, sometimes a smell of hot plastic.
Open the module and look for burn marks on the resistors.
Find and fix the short first, then repair or replace the module.
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 dead
Brake, reversing and fog together is the module fuse; one side's tail lamps is that side's fuse; only the high-level lamp is its lamp or relay.
freeLook at the bulbs with a helper
Engine running, pedal pressed. All four brake lamps, both bulbs in each cluster.
freeTest the fuses live
Heelboard boxes under the rear seat cushion, the engine bay boxes and, on 1995 cars, the boot box. The numbers are in the fuse block below.
a test lampCheck the high-level stop lamp
Is it secure, and are its wires whole under the shelf?
freeCheck the bulb wattages
Mismatched or wrong bulbs set the warning without anything failing.
freeOnly then the module
Look for scorched parts on its board, and find the short that caused it.
a used moduleThe 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, 1995 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.
Circuit descriptions from the Jaguar fuse tables, 1995 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.
These positions are not on the drawings above — find them on the legend printed on the lid of the box itself.
What it usually isn't
Don't spend money here first:
If none of this finds it:
On jagaux.com
- Jaguar XJ6 (X300) Headlights Not WorkingIf the headlamps went out as well.
- Jaguar XJ6 (X300) Gearbox ProblemsIf the lever won't leave Park though the brake lamps work.
- Jaguar XJ6 (X300) Instrument Cluster, Dash LightsIf dash lights failed together with the rear lamps.
- XJ6 (X300) fuse boxes and relaysRear lamp fuses for 1995 cars; 1996 and 1997 from the same page.
- Jaguar XJ6 (X300) Turn Signals, Indicators Not WorkingIf the indicators are dead or flash fast rather than the brake lamps.
- 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.