I was driving home the other night and my head lights started to dim. I thought I had an alternator issues so I got home as quickly as I could and parked the car hoping to save some of the battery. The next morning I needed to get my other car out of the garage and went to move the jaguar. No power I had to use the key to open the door. As I sat in the car I heard a "click" and the lights came on and the car started right up. I moved it into the garage and turned it off. Power was then gone and the antennae wouldn't go down. A week later back from a trip I went to start to figure out what was wrong, very dim dash lights, wouldn't start. Went the next day, no issues, started right up, I turned it off and dim lights no start. Has anyone had this happen? It seems like there is something keeping full power from reaching anything but it is intermittent and then works. Any help would be useful and at least provide me somewhere to start.

 

You may have a loose or corroded power connection, possibly one of the 12V feedthroughs in the engine compartment firewall, or loose/corroded battery connections - start there.

 

Had the same issue with my xj8. Like quad said, start at the battery, clean and tighten the connections, go to the ground point to the right and do the same, follow the + to the box just above it and insure the links are intact and everything is clean and tight. Just be methodical and follow the cables, it isn't too bad on these cars.
There is a grounding strap under the car near the right front footwell you can check.
Where the 12v + comes through inside the engine bay between the ECU and shock tower (LHD car) is where mine was loose.

We usually do Porsche work and on those cars I always add a ground from the negative post on the batt to the engine block. I added one to the xj8 as well. For safety and reliability it is cheap and easy insurance.

 

Thank you the help. I started at the front sinceni had already checked the battery and when I found no issues I went back the battery. The negative cable was burning hot so I disconnected it and clean everything again, put it back on and no more issues.

 

Dude, same thing happened to me. I replaced the ground from the battery with an old-style cable (not a braided cable), as well as the ground that goes from the body to engine/tranny under the right front footwell. I just wanted to eliminate those two cables as possible problems and a lot of weird stuff has gone away. The hot cable is a dead giveaway.

 

I love hearing about simple solutions... with this car they are so often NOT so easy! Good job.