There is a connector ( BT - 4 ) above the fuel tank that may not be fully engaged

It is the same as the LS3 and RS3 and others , different wire colors

This connector if handled to hard can break the external lock pins , so caution before you remove it

You can visually ensure the tie wrap is on the lock over bar

This connector has a lot to do with your SLCM and the immobilizer decoder module ( located in the dash , pic from Brendan , but you need not get to that to ensure it is powered ) for the chip in your key

My brain hurts , nap time

 

Any results ?

Probably need to spend time identifying the connector / wire colors in your pic

Your SLCM is located to the car's left of the fuel tank under the fuel cap well

There will be positions for 4 connectors on the SLCM

Try to read the SLCM part # as there are many for the different regions of the world , they have been mixed

Genuine Security/locking Module For Jaguar Xj 1995 - 1997 (from 720125 To 812255) Classic | Jaguar Land Rover Classic Parts

Click on the # 1 icon square

The SLCM does not need programing / software before install , just FOB initializing , you should have early 315 MHz FOB on the FOB battery cover

18-09 Keyfob Transmitter Battery Replacement.pdf (jagrepair.com)

Some have placed in batteries in backwards and only use good quality batteries , there are repair parts ( switches and rubber button covers ) on E - Bay

Your 2 left and right door key barrels is a factor in SLCM part # ( one of the SLCM connecters wiring ) as there are normally just the driver door , early year and region / market / country version

If you reconnect the SLCM you definitely need to remove the battery positive post

There is a hard reset of the SLCM that has worked for me , but all connectors have to be in place

 

Thank you for all this information, very much appreciated. I haven’t been able to test any of this on the car yet but will try at the weekend and report back.

 

Ok not had a great deal of time to work on the Jag recently but I did try to plug in a scan tool into the OBD2 socket and my scanner could not connect? The ECM also has a very rusted casing and when I opened it up there did look to be moisture but not actually wet. All over the plug connections and pins on the ECM are good. I did speak to a Jag specialist and they that I will have to the exact part number ECM for it to work?? And the same for SCLM as they said that it would need to be reprogrammed?? Has anyone else had any success with either getting the correct part number modules and just plugging them in or even had different part number that actually still work in the car.

The ECM is LNA1410BF
SCLM is LNA2600CB

 

On the later X308 things needed to be loaded operating software but not on the X300

Both the ECU and SLCM are region specific so you would be looking for the British version

On the SLCM there is the concern if the car has 2 door lock barrels left side and right

There is a fuse for the OBD 2 reader port and if your fuel pump naturally comes on the fuse is intact as the same fuse for fuel pump control

Right Heelboard fuse box # 10 , this fuse requires the relay in the corner of the fuse box to close

SLCM :

Genuine Security/locking Module For Jaguar Xj 1995 - 1997 (from 720125 To 812255) (x300) Classic | Jaguar Land Rover Classic Parts

ECU :

Is yours a 3.2 or 4.0 liter ?

Genuine Electronic Control Module-3.2 Litre (3.2 Litre) For Jaguar Xj 1995 - 1997 (from 720125 To 812255) (x300) Classic | Jaguar Land Rover Classic Parts

 

Mine is a 3.2L and im pretty sure it has key barrels on both sides.

So if I did get replacement modules with exact matching part numbers would it all work without any other programming?

Due to the amount of moisture inside the can from being stood for a long time with water getting into the cabin im convinced that there may be a connector that is just wet giving a ground when it shouldnt.

In simple terms is there a check that I can do on the ignition switch or something that will tell me if I have a short to ground when I shouldnt?

 

There is a hard reset of the SLCM once those connectors are dry

There is a precaution for non USA models as this would lock out your stereo head ( theft protection )

This reset will not effect or reset the engine ECU

There are some clues if you are getting everything ( immobilization ) with key rotation

The 2 key barrel version has a different wiring at the SLCM connectors and the 2 key barrel models went to different markets and the parts # list may not be fully accurate

The person that messed with yours may not have been aware of that

 

So I managed to get a bit of time on the Jag this evening. Ive been looking at the ignition switch and testing the pins on each position of the key. Im not brilliant with wiring but here are my results.

One lead from my multimeter was connected to a ground on the car and I have as follows.key in ignition but not turned

12v on white and brown

11.75v on white and orange

10.96v on red

2.8mv on blue



With key in pos 1 I have



111mv on white and brown

11.75 on white and orange

10.88v on red

83mv on blue



With key in pos 2



264mv on white and brown

255mv on white and orange

10.6v on red

125mv on blue



On crank



11.7v on white and brown

200mv on white and orange

200mv on red

45mv on blue

can anyone shine any light on weather this is correct or something a miss?

 

Uniformity the ignition swatch when putting a meter on it is not the most confidence building , ask me how I know

But fortunately it can be replaced without needing a new key as the barrel stays in place and the switch removes as in this pic from someone else

Pin 5 will be a car frame ground that can be affected by the ground connection being disturbed.

I had some green corrosion on my pin 5 , drink beverage spills into there

This ground is always present and should be close to 0 resistance

Correlating your information against a wiring guide

Editing

Your pin 5 should never have a voltage

To make it easier to work on , the switch side connector can be removed to bring it out to you . the connector mount lifts straight up to remove

I think your engine light going out is normal

 

Im still unsure if the voltage readings Im getting are what would be expected for each key position. Does anyone have an idea of what wires on the ignition switch should have voltage and when

 

The ignition switch when maked in the different positions make the voltages go to 0 grounding out though pin 5

The purpose of the switch is to command the relays around your car to close by grounds provided by the ignition switch

A way to test the ignition switch without a meter is to have the key in the run position and as you remove the relays in the corners of the fuse boxes the relay should click in your fingers back to open

the exception is the left engine bay fuse box , is the car horn , swapping option


Ask questions

There is the notion of feeler voltages but they are looking for a ground for the device to come alive

An example is when you remove the key it makes a linier switch to command the SLCM to go into a all locked up sequence

This linier ignition switch can freeze up and there is a simple test to see if

This would be pin 4 to 5 going to 0 resistance , or the seat and steering column moving on key removal

 

It could be the SLCM is stuck in the car exit mode and not the car entry mode to start ( SLCM required ) and drive away

Do you have a battery draining as it sits overnight ? This is known as a parasitic drain and common as the SLCM gets stuck and does not go to sleep , pin 4 to 5 of the ignition switch connector and door lock agreement switches , Brendan / B1MCP found a connector