Can someone please help identify which of these relays is the one that controls the security system on the X300s? It was suggested to me that it was the “blue one”, but as you can see from this photo from our XJR, they all appear to be blue. Please help…

 

A few points to clear up, John:

The blue items you see are the relay sockets, whereas the actual relays above them are black. You also have a yellow socket/gray relay and a brown relay in the fuse box in the photo. None of those relays are related to the security system.

The security system does not have a particular relay; it is always powered. It only has a fuse, which is fuse F4 (red, 10A) in the trunk fuse box.

Fuse F1 (blue, 15A) in your photo is for the "central locking", and so is related to the security system. The relays for central locking are in the Left Hand rear heelboard location.

What sort of problems are you trying to sort out? Many have had issues with the security system and central locking.

 

Richard,

The main issue we’re having with our ‘96 XJR is that the key fob can’t lock/unlock the doors, nor open the trunk. However, when we go to unlock the car with the key in the driver’s door, only the driver’s door unlocks. The other three doors are not affected.

Although it might be unrelated, after all this started happening, the car’s horn will frequently (approximately 5-10 minutes apart) without any manual actuation of the horn.

Thanks

 

Hopefully you already know this, but holding the key in the unlock position OR turning it twice to the unlock position is supposed to unlock the other doors.

"Twice" is a funny word, isn't it.

 

A reason for the key fob to stop locking the doors could be that the key barrel switch is jammed.

( Taken from Jaguar XJ6; Jaguar X300; not starting; start)

The Ignition switch

We all get used to thinking of the switch only working in a rotary fashion, but it doesn't. The lateral part of its movement (along the barrel axis) has a switching function too, and for sure that function switches power to things like the electric seat entry function, i.e. before the key is rotated to the first position.

Often, one of the relays behind the RH front headlights stays live all the time if this part of the switch is not cutting the power, draining the battery. If this relay remains closed, the ECU thinks the engine is still running so the car won't start.

Sometimes it is only necessary to remove the switch and free up the lateral function with WD 40 or similar, unless the spring is broken, in which case you'll need another switch.

If you want to prove/disprove this theory before committing to any real work, disconnect the ignition switch before leaving the car overnight.

Door locking with the fob

When the engine is disabled in this way (at least by this ignition switch lateral movement fault) the doors and boot cannot be locked with the fob for the same reasons that they cannot be locked if the boot lid or doors are actually left open. The locking procedure only works when the ECU relay is off (not powered) but won't work if the ECU relay is powered when a request to lock the doors is put made by the fob. In this case, you will hear a refusal 'peep' from the security horn. It follows that a similar problem will be encountered if the boot switch or any of the doors switches are broken, not reporting to the system that they are in fact shut.

Removal of the ignition barrel to free up the igntion switch is done by putting the key in and turning it to position 'I', and then pushing in the little detent pin on top of the outer barrel with a bent pointed tool. The lock barrel can then be pulled out, exposing the laterally moving part of the ignition switch. Naturally the column shrouding will have to be removed to do this. An alternative method would be to remove the ignition switch itself and free it up or fit a new one.