Jaguar XJ40 Power Aerial Stuck
Usually it's the cheapest part: a mast costs about £15–20 and on most cars goes in from outside in 15–30 minutes, the radio driving the old one out and the new one in. If the motor winds but nothing moves, I'd open the unit next — a broken belt, a snapped cable or a cracked joint on its board — before touching the relays in the boot.
How bad is it · Safe to drive
Safe to drive
A mast stuck up is at risk in a car wash or a garage door; otherwise this costs only reception.
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 dirty, bent or worn mast
Grit and old lubricant clog the telescoping sections. A slight bend, even at one joint, is enough to make it bind, and once a section sticks it tends to come back. Paint overspray or a hedge brushing the mast does the same.
The motor runs but the mast sticks, needs a push, or stops short — halfway, or a few inches from fully down.
Extend it and look along each section for a bend or flat spot, especially where it stops. Wipe it upward only, with alcohol; wiping down drives the dirt into the joints.
A new mast, not a motor unit: nut off at the wing, radio on to drive the old one out, feed the new toothed cable in, radio off to draw it in — about 15–30 minutes. A seized mast can often be freed first: oil or penetrating fluid worked in while it retracts, then wiped off with alcohol and finished with silicone or dry graphite. Masts without the motor are cheap from Jaguar parts specialists, around $12, with a new grommet for a few dollars.
A broken drive belt or worn drive wheel inside the unit
The Hirschmann unit drives through a small toothed rubber belt, and a small wheel holds the cable against the drive gear. A broken belt or a wheel worn flat lets the motor run without moving the mast. Water getting into the housing is often what finishes the belt.
You hear the motor wind after radio-on or radio-off, but nothing moves. Continuous clicking at full travel means the drive is jumping teeth; a two-part drive wheel that has split can drive up but not down.
Open the unit and look at the belt, the idler wheel and the drive wheel. Do it before buying a mast — a new mast won't cure a slipping drive.
A replacement belt from an aerial specialist — there's no Jaguar part number, and generic audio belts may fit. For example, one Hirschmann belt measured about 5.25 mm wide on a 2 mm pitch. A flat idler wheel can be built up and filed round.
The toothed cable snapped inside the motor unit
The mast is driven by a toothed nylon cable. When it breaks, the broken end stays wound inside the drum, a new mast can't engage, and a jammed drum can blow the fuse.
Look at the end of the old cable: square means it broke and the rest is inside; pointed means it's intact. Grinding for about 15 seconds after radio-off with no movement points the same way.
Square end: the unit comes out of the boot and is opened to fish out the broken piece. If a new fuse blows straight away, the drum is jammed. Getting the unit out: strip the right-hand boot side lining, unbolt the motor's earth strap, unplug the coax and the power plug, loosen — don't remove — the two nuts at the base (8 mm; the mast nut at the top is 12 mm) and pull the assembly down and out.
Remove and open the unit, pull out the broken nylon, clean out the old grease and any bits of broken plastic gear, re-grease, then wind the new cable onto the gear by turning the motor by hand. Allow 30 minutes to an hour.
Cracked solder joints on the aerial unit's circuit board
The unit carries a small board. The joints round its thick wires crack, and water in the housing corrodes the rest; the motor goes silent or runs one way only.
12 V at the aerial's connector but a silent motor, or it retracts and won't extend; the boot relays click.
Prove the supply at the plug first. Then open the unit and look for cracked joints and water marks.
Wick off the old solder and resolder fresh — just reflowing the old joints tends to fail again within months. Failing that, a known-good used unit. While the unit is out, renew the rubber grommet where the mast leaves the wing — a perished one is how the water gets in. It goes in far more easily with the unit out: soften a stiff new one in hot water, ease it with soapy water, push it into the hole from outside with its sloped lip matching the wing, then push the mast up into it from inside. Use a wooden stick, not a screwdriver, near the paint.
A replacement aerial that doesn't speak the car's language
Until the 1994 Harada unit, the motor is driven through an up relay and a down relay that reverse its polarity, pulsed for about 15 seconds by the central processor; the original unit slips at the end of travel. Universal aerials expect a steady trigger wire and their own end stops. An aftermarket unit wired for 1993–94 cars won't work on a 1988–92 car, and a European unit on a US car differs again.
A new or used aerial does nothing, rises only with both leads powered, won't retract, or keeps blowing its fuse.
Measure which lead is live after radio-on and which 15 seconds after radio-off. Know your car: from VIN 667828 the relays moved into relay module K, and from VIN 687219 (1994) an integrated Harada unit replaced the relay pair.
Safest is a genuine unit, new or from a breaker; Hirschmann units of 1988–94 interchange if the plug is swapped. Otherwise a relay interface board, or the old unit's board moved into the new aerial. Two diodes in the up and down leads work on some cars and blow the fuse on others. With an aftermarket radio, a switched 12 V feed instead of its weak aerial output.
A new mast that hasn't caught the drive
The processor only runs the motor for about 15 seconds. If the new cable is fed in late, or teeth the wrong way, the timer stops before the mast is home, or the gear clicks over the teeth.
Straight after a mast swap it stops a few inches short, clicks loudly at the ends of travel, or won't draw in at all.
Radio on to push it back out, then check the teeth face the right way and the nylon is fixed firmly at the mast top.
Worth trying: feed the cable teeth forward the moment the radio goes off and keep pushing until it bites; cycle the radio once or twice. If it still won't catch, turn the gear by hand with the unit open to wind it in.
No 'up' signal from the radio or the processor
The radio puts 12 V on the Light Green/Black wire while it's on; the central processor turns that into a timed pulse to the up and down relays, which feed the motor on Green/Red (up) and Green/Blue (down). A radio that doesn't send the trigger leaves a perfectly good aerial silent.
Silent motor and no relay click at radio-on or radio-off, often after a radio has been changed. On one car the mast went up as soon as an open door was closed — try it with the doors shut before testing anything.
Put 12 V on Light Green/Black at the boot: if the aerial runs, the radio isn't sending. Put battery voltage straight on the motor wires, then swap them — it should run both ways. Retracts but won't extend: check the 12 V feed to the up relay and the earth at the down relay. These circuits are switched on the earth side, so a stray short to earth — a screwdriver arcing near the boot lock, for example — can upset them; look for damaged wiring in the boot if it stopped after work there.
Worth trying: plug in the aerial lead at the radio harness if it's loose, fit the right radio (DBC11303 for 1993–94; DBC6436 looks the same but is earlier), or feed the aerial from a switched supply.
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.
Listen at the aerial, radio on and off
About 15 seconds after radio-off the motor should run. Runs but no movement: belt, wheel or cable. Silent: supply or the unit's board.
freeClean and inspect the mast
Extended, bottom to top, look for bends. Wipe upward with alcohol; oil only to free it, then wipe it off and finish with silicone or dry graphite.
freePull the old mast and look at the cable end
Nut off, radio on. Pointed: feed in a new mast. Square: the unit comes out.
freeFit the new mast on the timer
Teeth facing the right way, fed in as the radio goes off. Stops short or clicks: push it out and feed it again.
£15–20Prove the motor and its supply
Battery voltage straight on the motor wires, then reversed. If it runs both ways, check 12 V at the plug on radio-on.
freeNo supply? Check the trigger before the relays
12 V on Light Green/Black from the radio while it's on. None there: radio or its harness plug.
freeOpen the unit: belt, drive wheel, board joints
Look for water inside. Resolder with fresh solder; clean out old grease and re-grease the gears.
free, an hourFitting a different aerial? Match the control
Relay-driven cars need a relay board or diodes for a single-trigger aerial; a genuine unit avoids it.
cheap partsWhat it usually isn't
Don't spend money here first:
If none of this finds it:
On jagaux.com
- XJ6 (XJ40) fuse boxesOther years from the same page.
- XJ6 (XJ40) 1993–94 radio pinout and wire coloursThe aerial trigger wire at the radio.
- XJ6 (XJ40) 1991 radio pinout
- XJ6 (XJ40) 1990 radio pinout
- 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.