Hi,

I've noticed recently that when I leave my lights on auto, the battery drains overnight. If I switch them off, it doesn't drain.

Can anybody think of anything obvious that could cause this? The lights themselves do turn off once the engine is off ( on auto ).

It's a 1998 XK8 Coupe, UK.

 

Do you lock the vehicle?

 

I almost always do - I'm pretty sure it was locked earlier.

I should add, I had Halfords check the battery a couple of weeks ago and they said it was as good as new. I'm pretty sure the alternator is ok too - it shows as 13v on the dash sensor, and the battery got to half full on the drive to Halfords after a jump start ( from empty enough that the lights wouldn't come on ).

 

I've been informed by SWMBO that the car was definitely locked earlier ( the last time I used the car before I found it was flat was Saturday ).

 

Your statement above provides the clue.

The electronics will often not reset properly after a jump start to a dead battery. Disconnect the battery for 30 seconds then reconnect it to reset everything.

You also would be well advise to charge the battery. A 'half full' battery on this car is inviting electronic problems. Also the dash meter is highly inaccurate, and with a weak battery the voltage can drop very low during starting, corrupting the operation of the electronics.

 

Thanks, I'll give that a try, although 'half full' was what was measured by the battery tester at Halfords ( ~400 of around 900~, although I don't know what units ). I then drove the same trip home, so I'd imagine that the battery should have been roughly full by the time I got home.

Is there any way once I've reset the electronics that I can test the battery isn't being drained other than by seeing if my battery is dead the next day?

 

Ideas:
1. battery no longer holds charge no matter how you charge it - common and causes problems
2. some other fault - on an S-Type the sorts of places to look are the flap where the key goes in the ignition and the stalk for auto lights (whose wiring chafes)

 

Some of these may or may not apply but here for reference.

bob gauff

 

Appears this has been happening to my car all along. I have just resorted to always using a trickle charger at home.

I notice that there is some quiescent current by looking at my DRL's. I replaced them for LED bulbs, and they keep being lit a tiny bit at all times.

I just tried setting the stalk to Auto yesterday, and after a couple of minutes the LEDs now go out.

So, appears that I should install this link lead. It just appears to be a diode? Would it be ok to just splice a 1N4007 or something in there? (In what direction?) Looks easier than struggling with finding this overpriced cable.