1990 3.6 Xjs coupe.

i always disconnect the battery when parking the vehicle due to a parasitic drain.

i went out for a drive today, as I do weekly to keep the juices flowing.

after driving for 40 minutes, I parked up, came back to the car, attempted to start and I got the fast clicking noise that I would usually associate with a flat battery. I find it strange that I parked it up briefly and it won’t start now. The battery is old and could do with replacing. However what else could it be? Is the starter motor linked to the headlight relay?

 

Start with the most obvious, I.e., the battery. For whatever the reason, these Jags are very sensitive to battery voltage.

 

Check that the boot light switch is actually turning off the lights; if not, a rubber pad glued to the lid to ensure the switch actually does go off will usually do it. Starter not linked to the headlights. The noise is the solenoid jumping in and out as there is enough juice to activate vit; but not enough to keep it in once the starter load gets on the battery.

 

Hello

Talking from experience on my commodore (not my Jaguar). I did one of our weekend drives and stopped for fuel, it only just started. Purchased a new battery and put it in the boot as a spare. Had no issues and eventually gave the spare to my son.
Some time later, had a no start with the battery again and had to jump start her, and I drove to the battery place and again - put the spare battery in the boot again as it behaved herself again.
I did replace the battery eventually, but it would have been a least 1 year, maybe 2 since the first issue, so I suppose the moral of my story is the battery can play up before they actually die out

My commodore had the battery in the boot as well, (upholstery had to be removed to gain access). And the voltage drop was also also a known issue for them

Cheers
Steve