I have a problem with a 2001 S type (v8)that has intermitment (about once every two weeks) dead battery. Battery replaced several times. No warning lights or check engine issues. No connection with days driven or not driven. Battery shows no sign at all of weakness in the morningsthen sudenly one morning its dead...totaly dead. This has been going on for about 6 months.
When jumping the battery the alarm almost allways sounds when opening the door and lights flash...The only system not functional on the car is the back-up warning sensors.

Any ideas???

 

Wow..you guys are great. I did in fact find an exta wire in the trunk about a month ago...just hanging down with white connector. It was completely corroded - even impacted with crud. I cleaned it out with a scribe and tucked it away. I will go cut it off...can someone tell me what that lead is for??
I do own a multimeter and know how to use it...I've been suspicious of the glove box light and trunk lights but they seem to working everytime I look into them as culprits. The ignition barrel seems like an interesting culprit..is there a trouble-shooting method to checking that...As far a techinal advice..I've worked on my own cars for 20+ years (jags for zero years). I would self-rate my knowledge as -Troubleshooting knowledge 8/10. tools 7/10. Knowledge of Jag electical system 1/10. This one is kicking by butt. By the way, what section of the electrial harness are we talking about replacing- and what is the failure mode inside that harness that causes this in other cars?? Very very much appreciate the help thus far.
Last thing..can someone confirm with me that the alarm going off after connecting the jump cables has nothing to do with this.

 

I don't see an answer to this last post. Any further info on this problem, and what is that white wire in the trunk for?
I have just purchased a 2000 S-Type and the battery went dead after the car was parked in the garage for two days.