Morning all!

I recently sold my X300. Sods law, on the very day it was sold it's begun having issues!
The issues are intermittent - The person I sold it to encountered them twice in 2 days - But they seem to be getting increasingly frequent since it was brought back to me

When the issue is ongoing, various electrics don't work. These include headlights (Though on occasion, rear lights seem to work), wipers, courtesy lights, boot (trunk) lights, outside and cabin boot release buttons, indicators and the shift lock solenoid. At this point, the car will not start when the key is turned to position 3
If the car is locked, it can be unlocked with the key fob, but can only be locked with the key. When locking and unlocking, the alarm does not chirp. If the car is left locked, sometimes the alarm start sounding after a few minutes
Radio, HVAC system, engine fan etc. All work fine

I replaced the BPM with one from another car (with the same /001 suffix on the code) and straight away the interior lights came on and everything else worked as it should, the engine once again fired up. Giving myself a pat on the back I turned the car off and locked it (with the fob!), only for the alarm to begin sounding as I got back to the house!!
Once again, the car will not start and various electrics don't work.


I've checked the white plug on the front right of the car (When unplugged, the engine fans stopped running), and the large black multiplug on top of the fuel tank (Which seems to be held closed with a cabletie, but no amount of wiggling put any life back into the car)
I'm unsure where to go next on this issue, can anyone advise?

 

Do not over tighten the battery post bolt , it can split the special shaped nut underneath

Right at the battery and the cable turns down there is a fuse box that the terminal nuts can come loose

You can remove the battery cables from the 2 large terminal post on the rear fire wall but only after removing cable

wiggle the post to see if the connection is loose behind the sheet metal but only after removing cable

There is a 3rd post on the rear of the right wheel well that is the starter / alternator connection

At the rear seat behind your ankles there is 2 covers and the battery cables have terminal nuts there as well but all you do is ensure they are tight

There is another junction point when you remove the rear seat pan but we'll save that for later

So now we will look at the relays that control a section of power

These are the relays in each of the fuse boxes ( 4 not including the left engine bay fuse box , horn ) that are controlled by the ignition switch

The one in the left engine bay fuse box only runs your horn so is a swapping option

With the key in the run position before starting the engine you can go around and remove the fuse box relay and feal for it to click

This will be the relay returning to the open position

If it does not click swap it

If it does click it can still be bad on the inside so swap it and run your systems

The big BT4 connector above the fuel tank is going through a couple of layers of sheet metal and the cutout can keep you from making a full connector mating but you have to be careful and not break the lock over pins

You can also have a open cell on the battery , never install the battery in backwards

 

Parker, thank you very much for your suggestions. Unfortunately these didn't work for me.

HOWEVER! I did manage to find the resolution, and as far as I can see, it's a new one to the Jaguar community.

Because I have a scrap car, I'm plessed with being able to swap and change parts for free. In this case, a friend of mine with an XJ40 had previously had issues with his boot (trunk) fuse box, causing weird issues.
I changed this, and the car worked! All electrics etc. work, and car will fire into life as it should. But wait...

I closed the boot, locked the car and the issues began again..
I disconnected and reconnected the rear fuse box and the car worked once again. Weird.

Knowing that the 'Boot open' light used to occasionally flicker, and that it routes through the rear fuse box, I changed changing the boot closure micro switch out. So far the issue seems to be sorted!


A weird fix, but one I felt was worth sharing with the community. I hope it helps others with strange no-crank issues!
Any further issues, I will of course report back.

 

Along the trunk right hinge cover there is a history of the wire bundle chaffing and this may have caused the security system when seeing a trunk open position or trunk commanded to open to be out of expected sequence

It's an easy check and you may nail it down as that's it

The security system would keep certain things from operating in your list ( the starter for sure ) and probably all your other things

The rear fuse box as where the security system gets it's power so it may have re - booted

Most of the fuses are hot at all times as they bypass the relay in the corner and the only fuses that rely on the relay to close are 10 ; 12 ; 14 ; and 16

The Security Lock Control Module is fuse X so it has a direct battery cable connection

You may have had a trunk release solenoid and worn linkage that is not working % 100 all the time throwing a monkey into the works

Both of these items along with the wiring to them at the hinge have a history