Jaguar XJS Window Motor, Windows Slow or Not Working
On the XJS, when both door windows die together it's usually the feed — the window relay or the thermal breaker, since on 1988–94 cars the circuit has no fuse. A single slow or dead window is most often worn switch contacts, dry tracks, or on 1988-89 cars the weak square-case Delco motor. I'd check for 12 V at the switch socket before taking a door card off.
How bad is it · Safe to drive
Safe to drive — but a window stuck down leaves the car open
A dead window doesn't affect how the car drives. A window stuck open lets in rain and thieves, so get it closed before parking outside.
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 window relay — both door windows die together
On 1988–94 cars the door windows have no fuse (1987 and 1995–96 cars do have one in the panel). Power comes off the battery post on the right of the bulkhead, through a thermal breaker, then through a relay that only closes with the ignition on. When that relay dies, both windows stop at the same moment.
Both front windows dead at once, switches doing nothing; often after the car has stood in rain.
With the switches out of the console and the key on, the Brown/Blue wire at each socket should carry 12 V. If it's dead everywhere, check the relay: 12 V reaching the coil but none at pin 87 means the relay. On a 1989 it sits behind the glovebox with three wires — white/pink, brown/blue and black.
Fit a new relay; it is an ordinary automotive part, not a Jaguar one.
The thermal breaker in the window feed
The breaker protects the motors when a window jams. It wears out from long service: a motor fed through dirty switch contacts labours, draws more current and keeps tripping it until it fails open.
Every door window dead, nothing else wrong. A window relay that clicks every few seconds while the glass barely moves is the breaker cycling: look for a binding motor or regulator, or a short to earth.
On a 1990 car it's a small black square with two spade terminals, behind the trim panel at the fuse access on the passenger side. It should show continuity; bridge its two wires and see if the windows come back. At the relay: 85 black, 86 white/pink, 30 and 87 brown/blue; dirty socket contacts cause trouble too.
Replace the breaker. A jumper across it gets the windows working while the part arrives, but don't leave it bridged.
Worn or dirty window switches — slow or one-way windows
The switches carry the full motor current, so their contacts burn and the grease inside them goes bad. A tired switch starves the motor, which then crawls, stops in one direction, or quits.
A window that's slow, works only when you press hard, or goes down but not up.
Swap the left and right switches and see if the fault moves. With the key on, push hard on the switch and wiggle it: a window that suddenly moves points at its contacts. Unplugged, 12 V straight on the motor pair should run it both ways — if it does and the switch doesn't, the switch is at fault.
The switches snap apart: clean the parts and refit the small pieces in their original order. Polish the contacts with a pencil eraser and contact cleaner rather than sandpaper, which strips the plating. Replica switches fit the bezel and can make the windows noticeably quicker.
A weak window motor — especially the 1988-89 square-case Delco
The square-case Delco motor of 1988-89 is a weak design: worn brushes and commutator leave it short of torque at the top of travel, and its cover is held by two bolts in soft alloy, so the rear one works loose and the rotor wobbles. The motors have no end-stop switch either; a worn spring or rubber spider can jam the worm wheel so a good motor looks dead.
Slow over the last couple of inches, stops part-way, or only runs after you thump the door. A loud click and a jam right at the top. A window that sticks closed after standing in the sun can be a motor that always stops at the same point and has burnt that part of its commutator.
Door card off, unplug the motor and feed it 12 V and earth directly, both ways round. No movement at all means the motor or a jammed gear; try turning the output by hand while powered. Test the plug again with the window trying to move: a good reading with no load proves little.
A larger bolt with a nut behind it, in place of the loose cover bolt, can be fitted without taking the motor out. For a lasting cure fit a used pre-1988 round-case Delco motor with its regulator: it bolts in and is far stronger. Other cures: the armature, brushes and holder of a GM-type replacement motor (Cardone 42-126) moved into the original housing; or the Bosch motor fitted from 1990 (0 130 821 298 left, 299 right), which 1988-89 doors take with the later regulator and a bush-and-bolt kit (BEC10006/7KT). Many modern aftermarket motors don't fit; an older-style motor and regulator assembly does. A short piece of soft tubing in the channel above the glass softens the landing and moves the stopping point.
Dry tracks, glides and runners make a good motor labour
The glass rides in side runners and, on facelift doors, a bottom track with a plastic slider that carries most of the load. Dry or worn tracks add enough drag to stall the motor, and a new motor in the same tracks will struggle the same way.
A window that labours, stops at the same points, or won't close fully even after a motor change.
Have someone lift the glass gently while you press the switch: if it then runs, the drag is in the tracks. Look for a worn bottom slider and a runner whose lining has come loose.
Clean and re-grease the glides and the bottom track — silicone paste worked in by hand, or silicone spray on the runners. Replace a worn runner. Renew the door's plastic vapour barrier while the card is off.
Convertible rear quarter windows — the motor gearbox
On the convertible the small rear windows are driven through a gearbox with a rubber insert that cushions the end of travel. The rubber perishes, the gears jump at the stop and wedge. A set screw on the worm can also tighten over the years and bind the gears.
One quarter window stops rising with the top; the other still works. Erratic travel, or a window that runs again after a tap.
With the rear trim off, look at the gears from above the glass. A 30 A fuse that blows when the console switch is held points at a seized mechanism. Inside the motor, look for a destroyed six-point rubber star, grease on the commutator keeping the brushes off, and the motor's built-in thermal cut-out.
Re-mesh jumped gears by twisting a long screwdriver between them. Back the worm set screw off until the teeth rattle, then in until the rattle just stops, and lock it. Hold a displaced rubber insert and its cap in place with small clamps. Worn brushes can be renewed. Tired built-in cut-outs have been replaced with 15–18 A ones. Early cars use a Delco quarter motor, later ones a Bosch like the door motor but with a 14-tooth pinion where the door's has 8 — for example Bosch 0130821018.
No relays in the window circuit — slow windows and short switch life
From the factory the full motor current runs the length of the car through the switches. The long wiring loses voltage under load, so the windows are slower than they should be and the switch contacts wear out.
Windows that work but are slow on both sides, with 12 V reading fine at rest.
Measure the voltage at the motor while it is moving, not at rest; a big drop under load is the sign.
Worth trying: add relays so the switches only trigger them — two ordinary relays per window or a window-lift relay — with heavier, properly fused feeds into the doors. Speed and force can roughly double.
Convertible quarter windows — the top sequence, relays or control module
The rear quarter windows are not on the door-window circuit: the convertible top's control module raises and lowers them through its own relays as part of the top cycle. An incomplete cycle, a bad relay or the module itself leaves them down.
Quarter windows stay down while the top and the door windows work; both stopping at once points at the control side.
Run the top fully down, then fully up — the windows only rise near the end of closing. Swap the six identical relays by the top pump in pairs and see if the fault follows; on 1988-91 cars they sit on the right of the cubby behind the seats. If both windows die together and the motors run on direct 12 V, suspect the control module. If they died after console work, look for an unplugged connector under the armrest cubby and the ski slope; a dead cigar-lighter lamp at the same time points at a shared feed. The three centre switches are interchangeable for a swap test.
Worth trying: to lower stuck windows, pull the DOWN relays and bridge terminals 30 and 87, leaving the UP relays in, as they complete the motor earth. If the faults keep coming back, wire each quarter window to its own switch, fed from the front-window feed after the thermal breaker.
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 which windows have stopped
Both door windows at once points at the feed — relay or thermal breaker. One window points at its switch, motor or tracks. Quarter windows only, on a convertible, point at the top system.
freeCheck the feed at the switches
Lift the switches out of the console, key on: the Brown/Blue wire should show 12 V and the Black wire earth. On 1988–94 cars there's no fuse to find in this circuit.
a multimeterBridge the breaker, then test the relay
Jumper across the thermal breaker's two terminals; windows that come back mean a new breaker. If not, check for 12 V out of the relay at pin 87 with the key on.
a jumper wireSwap and clean the switches
Swap left and right and see if the fault moves. Clean the contacts gently — eraser and contact cleaner, not sandpaper.
free, or replica switchesPower the motor directly
Door card off, 12 V and earth straight onto the motor pins, both ways round. If it runs, the fault is upstream; if not, it's the motor or a jammed gear. Then re-test the plug with the window trying to move.
a pair of test leadsLubricate the tracks and runners
Grease the glides and the bottom track, check the plastic slider and the runners. A helper lifting the glass while you press the switch shows whether drag is the problem.
grease or siliconeReplace the motor with an earlier one
On 1988-89 cars, fit a used pre-1988 round-case Delco motor with its regulator — it bolts in and lasts. Bench-test it before it goes in the door.
a used motor and regulatorConvertible quarter windows
Cycle the top fully down and fully up, swap the six relays in pairs, then take the rear trim off and look at the gearbox before blaming the control module.
free to testWhat it usually isn't
Don't spend money here first:
If none of this finds it:
On jagaux.com
- Jaguar XJS Electrical Problems, Bad EarthsIf other electrics are failing too — earths and tired connections.
- Jaguar XJS Power Antenna StuckThe other small motor that tires with age; the same direct 12 V test applies.
- XJS fuse boxes and relaysWhere the fuse boxes and relays sit; other years from the same page.
- Jaguar XJS Convertible Top Not Working, Pump and RelaysIf the top itself won't move, or the quarter windows quit with it — switch, relays, interlock.
- Jaguar XJS Central Locking Not Working, Door Won't OpenIf the door lock is dead too: rods, clips and actuator behind the same panel.
- 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.