Jaguar XJ6 (X300) Headlights Not Working
When both headlamps or a whole beam die on these cars, it's usually a headlamp relay at the front of the engine bay, or the wire from the body processor that switches it. If the headlamps went together with the wipers, indicators and rear lights after fuel tank work, the big harness plug on top of the tank isn't seated. I'd check the bulbs and the fuses first, then the relays.
How bad is it · Garage, carefully
Fine by day — don't drive at night without dipped beams
The engine isn't affected. There's no dash warning for a dead headlamp on these cars, so walk round the car before a night drive.
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 rear harness plug on top of the fuel tank, after tank or pump work
A 48-way plug on top of the fuel tank joins the cabin loom to the rear harness. If it isn't fully home, the body electronics lose their links and the headlamps go dead along with much else.
Headlamps, main beam, wipers, indicators and rear lights dead together, no crank, selector stuck in Park — right after a fuel pump or tank job.
Look at the plugs on top of the tank before anything else; a plug that looks pushed in may still be half off.
Undo and refit the plugs on top of the tank, firmly, until they lock. Don't buy a body module or relays before doing this.
A headlamp relay, or the body processor wire that switches it
Early 1995 cars have a lighting module behind each headlamp; later cars use one relay for both main beams and one each for the dipped beams, at the front of the engine bay. The main-beam relay is the outer of two on the right, near the washer bottle, and its connections corrode. The relays are earthed through the body processor module.
Both dipped or both main beams dead at once, fuses and bulbs good; or one side only, with the main-beam lamp on the dash still lit.
With the relay out and the ignition on, the switching pin on the base should change when the lights are switched on. A reading stuck around 7 V points at the earth path from the body processor. As a test, earth the blue and white/grey wire from the relay to the module: if the lamps light, the relay is good.
Worth trying: clean the relay base and fit a new relay; if the switching wire never goes to earth, fit a used body processor module.
A failed bulb — the dash won't tell you
Each side has two lamps with a single-filament bulb each: the outer one is dipped beam, the inner one main beam. The bulb-failure warning watches mainly the rear lamps, so both dipped beams can die unnoticed. Tinted or high-wattage bulbs fail early, overheat the plugs and can overload the loom.
One beam dead with no warning on the dash; often non-standard bulbs fitted earlier.
Look at the lamps, not the dash. Bulbs are H1 on most cars; US cars use 9006 for dipped and 9005 for main beam. Check the plug for heat marks.
Fit standard-wattage bulbs of a good make, in pairs.
Slow to light: the light switch or the earth at the lamp
Each headlamp has its own earth terminal near the lamp. A loose or dirty nut there, or a worn light switch, makes a lamp lag by seconds before it lights.
One lamp, or both, comes on a few seconds late, usually the first time each evening; a new bulb didn't help.
If both lag, work the switch: lamps that come on at once when it's wiggled point at the switch. If one side lags, clean and tighten the earth beside that headlamp.
Worth trying: clean the earth terminal; replace a worn light switch.
Weak, yellow light: a fogged lens and reflector
With age a milky film builds up inside the headlamp, on the lens and the reflector. The lamps work but throw far less light, and the dipped beam's cut-off goes soft.
Lamps light, but the beam is short and yellowish.
Take the lamp out and look inside. On UK cars, check the dash beam-height adjuster isn't wound down.
Worth trying: wash the inside with a mild car shampoo, rinse, and dry it thoroughly. Don't rub the silvered reflector — it comes off.
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
Which side, dipped or main, and what else died with it. Headlamps plus wipers, indicators and rear lights is the harness plug; both of one beam is the relay.
freeLook at the bulbs
Don't trust the dash. Outer units dipped, inner units main beam.
freeTest the headlamp fuses live
In the engine bay boxes on both sides; the numbers are in the fuse block below.
a test lampAfter tank or pump work, reseat the plugs on top of the tank
Before buying any module or relay.
freeCheck the headlamp relays
Swap or replace them, and measure the switching pin with the lights on and off.
a relayClean the earth beside the headlamp
For a lamp that lags or flickers.
freeTaking a headlamp out
Ease the ball sockets free one at a time with silicone spray; the old plastic is brittle. A broken socket is replaced with adjuster kit JLM12118.
freeThe 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, 1996 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, 1996 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 XJ6 (X300) Won't Crank, Just ClicksIf it won't crank either and the lamps died at the same time.
- Jaguar XJ6 (X300) Alarm Keeps Going OffIf the headlamps flash or stay on with the alarm.
- Jaguar XJ6 (X300) Instrument Cluster, Dash LightsIf the panel lights go dark when the headlamps come on.
- XJ6 (X300) fuse boxes and relaysHeadlamp fuses for 1995 cars; 1996 and 1997 from the same page.
- 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.