I've had the car (97 Cabriolet) off the road for a few months as it needed a few bits and pieces doing. Knowing it was going to be sat I removed the battery and kept it dry stored and hooked up to a trickle charge with protector, diagnostics, etc. It was an almost new Yuasa so I expect it to be fine and the indicator shows it's all good.

Last night I dropped it back in the car, turned the key and apart from all the dashboard lights coming on, nothing happened. Not even an attempt at a crank. I put the charger on, left it overnight expecting it to be fine this morning. What I didn't do was disconnect it from the car...

Now, the battery seems to have less voltage than it did yesterday, which leads me to believe something is draining the battery whilst the car is parked. I'd suspected this before it came off the road too... As part of what I was doing I'd already disconnected the stereo and powered seats, so I know it's not those. My guess is the aftermarket Cobra alarm (an old version of their "basic" alarm) - what I don't know is where the module is, where it's likely to be connected or how to go about disconnecting it.

Can anyone point me to places it might be hidden?

Thanks

My bet would be the alarm too. The only way to find it would be to trave the wires from the fusebox. This should be obvious as they'll look different to the rest of the stock loom. 

Unfortunately these aftermarket alarms can be a problem. If you get a chance watch the old top gear challenge with the 3 series convertibles. Hamonds one had a similar problem. 

I'll be watching this thread with interest as I have a Cobra alarm fitted to my 1988 Coupe GT. I want to remove/replace it but the car works at the moment........

1 hour ago, athwyorks said:

I'll be watching this thread with interest as I have a Cobra alarm fitted to my 1988 Coupe GT. I want to remove/replace it but the car works at the moment........

It's booked for an MOT Saturday, then I'll be doing a driveway service and trying to trace the alarm sounder and module. Will update if that fixes the battery drain.

1 hour ago, Andrew Bell said:

It's booked for an MOT Saturday, then I'll be doing a driveway service and trying to trace the alarm sounder and module. Will update if that fixes the battery drain.

Please keep us posted on how you get on 🙂

On 6/25/2025 at 10:25 PM, Steve Q said:

Please keep us posted on how you get on 🙂

Complete lack of progress so far due to a combination of illness, being driven into in my other car and having to deal with that and a laundry list of other things which went wrong with the cabby and needed attention.

Passed its MOT with only a couple minor jobs... all the brakes, both front wishbones and a couple bushings. Almost got home from the MOT centre, stopped for fuel and it refused to start. Tried jumping with the aid of a friendly passing petrol head in an Octavia VRS - quickly deduced between us that the starter motor had died. The electrical burning smell and lack of any whirling were helpful in diagnosing that. Trailered it back to the garage, fitted a new starting whirler and for good measure a new battery. Whatever was draining the battery doesn't seem to be happening now - I'm wondering if it was just using a load of juice trying to turnover on a bad starter and then just not fully charging... or one of the other many and varied things that aren't working is what was causing it and it'll come back when they get fixed.

Going to start a new thread for all the issues...

Is the Cobra alarm still fitted Andrew? If so it suggests that the cure has been a new battery and a new starter motor.

Glad it's got an MOT and glad you've got the battery drain sorted. 

14 hours ago, cliffcoggin said:

Is the Cobra alarm still fitted Andrew? If so it suggests that the cure has been a new battery and a new starter motor.

Had most of the underside of the dash apart and the binnacle out and can't see any sign of an alarm unit. Can't find a sounder under the bonnet either... So either it's hidden under the centre console, which given how impossible that is to remove is doubtful, or I haven't found it yet... or, there never was an alarm and someone just tied the fob into the central locking to give it remote unlock. The search continues. What I do know is that the battery isn't draining at the moment...

The chances are that the battery was damaged while off the car, to the point where it could no longer hold a charge.