Disconnected battery, couldn't stop alarm going off!

[SimonR]

Much as the title suggests - I disconnected the battery today so I could work on the car, and the alarm immediately went off. I couldn't do anything to stop it so I reconnected the battery, at which point the alarm got louder, but I still couldn't stop it going off.

I tried locking/unlocking the door with the remote / key, starting the car etc - but couldn't get it to turn off.

In the end I disconnected the battery again and it stopped after about 5 minutes.

I guess this may be a case of RTFM, but whilst I'm waiting for a copy of the FM to arrive I thought I'd ask here.

Cheers for any insight you may be able to give

[Lucky]

What car were you working on?

[JimMann]

The alarm sounder has a separate battery pack inside it.
Jim Mann

[JimMann]

See article in the Modern XK column for February 2022.
Jim Mann

[SimonR]

Thanks Jim - I'll check that out!

Should have said - this is a 2003 XK8. I'll update my signature with that info.

[davidr]

Simon - in some ways this is good news. It proves that the battery pack in your alarm sounder is still alive and kicking. That's not always the case....

[andypryce]

Agreed, on the older XK8 there is something called the ‘intelligent sounder’ mounted beneath the offside wheel arch which is intended to sound the alarm if the battery is disconnected by thieves trying to disable the alarm. The same thing makes your alarm chirp when you set it. On most, mine included, the battery in it is long dead and it doesn’t work, so you are lucky yours is still working! I think you can stop it going off when you disconnect the battery by pulling the relevant fuse first, but I can’t remember which fuse it is, should say in handbook though.

[andypryce]

Meant inside the wheel arch behind the liner as the only thing beneath the wheel arch is the wheel

[SimonR]

Thanks for the replies, everyone!

So am I right in thinking that it going off when I disconnect the battery is correct and expected operation? I'm a bit at a loss because I couldn't stop it sounding. Also, my car doesn't chirp when I lock/unlock the doors.

I'm thinking that maybe the best thing is to pull out the fuse, or just disconnect the sounder (I found it when I took the wing off) and leave it be. I don't think that level of security is needed on a 20 year old car, and it sounds as though the batteries are very likely to fail and cause issues in the future anyway.

I'm just hoping that the rest of the security system is working fine when I re-connect the battery after I've rebuilt the front end next week!

[JimMann]

Hi Simon, as mentioned above, in most of the X-100 cars, the rechargeable battery contained within the sounder pack have long given up the ghost. It is a useful feature if maintaining originality, but given your starting point I guess that is not a priority. You could certainly disconnect or remove the sounder, but if it went off when you disconnected the battery during the strip down - as it is supposed to, then the batteries in the sounder are still good and should recharge when the main 12V battery is reconnected. It would not go off again unless you, or someone else, disconnects the main battery.

Choices, choices.

Jim Mann

[J80]

Unless you are keen on keeping the sounder, I would recommend you disconnect the sounder and battery pack and weatherseal the disconnected plug.

The batteries have a habit of going bad and creating a short circuit, which continuously blows the fuse that controls a number of other features in the car. It took me a while to trace this when it occurred to me - typically at the most inconvenient time.

[davidr]

Simon - I think you need to bear in mind that you are disabling part of the standard alarm system if you disconnect the battery. Your insurance group will be based on a standard car. Your insurance company will probably increase your premium if they know you've done that.
On the other hand you could not tell them but it gives them a reason not to pay out if you need to claim. And also consider that they hate what you are doing. In their mind, a written off car should be scrapped.

[SimonR]

That's a really good point, David - I hadn't considered the implications with regard to insurance..

I'm usually pretty pragmatic about things like this on my own cars and if it were a car I was planning on keeping I'd just unplug it and not tell anyone. As it seems to be working I'll leave it alone and adopt an 'if it ain't broke don't fix it' approach.

I'll monitor its function and if I'm at all concerned about the batteries then I'll replace them using the instructions in the mag - it'd be a nice bonus for the next owner.

I'll also read the manual about turning the chirp on so I can make sure it's working properly.

I've never had problems with previously written-off cars. The Rover that I've been driving for the last 7 years is Cat D and has been insured by several different underwriters with no problem at all.

Thanks for the input everyone!

[andypryce]

Personally I would just disconnect it, I tried replacing the battery in mine and it still didn’t work, it is a nuisance if it goes off every time you disconnect the battery, the main alarm will still work fine so I doubt very much if insurers would kick up a fuss.