Hi everyone!
I'm having a big battery drain on the X308 (4.0 1998). I measured it over 2 Amps, but that's with the doors and boot open. If I unplug the BPM fuse 5 it drops to 0.6A which is still a lot. I assume this drop is because the BPM cancels the door and boot lights so I'm down to hunting this 0.6A drain. I ripped all fuses out but other fuses don't seem to impact it, unfortunately.

From what I've read, my main suspect right now is the alarm horn going bad and messing with the electrics in some way. I can find threads on replacing it but I don't want it replaced, I just want it gone. I've located it but before I start removing stuff to access it: can I just unplug it or will this trigger all kinds of warnings? I don't want the car to go into panic mode because it thinks it's being stolen If it indeed triggers any warnings: can I trick the car somehow by i.e. looping the connector?

Also, is there a fuse/relay hidden somewhere I can remove to check if the culprit really is the alarm horn or will the batteries in the horn prevent it from ever being powerless?

 

I would look to the glove box and trunk (boot) light first. Both on the BPM

 

You do realize that the car needs some time (20 minutes?) to 'power-down' or 'go-to-sleep'.

The modules on the networks shut down one-by-one until the quiescent drain is about 31 milliamps.

You cannot test the electrical draw on the car until the modules 'time-out'.

I usually open the doors and boot lid then set the latches to CLOSED.
I then have access to interior electrics for testing.
Some component testing will 'WAKE' the car so you will need to start all over again with the wait.

 

+1 . . . all well covered in the Sticky section

 

I really appreciate your input put that doesn't really answer my question about the alarm horn BPM fuse 5 takes most of the lighting out of the equation and brings it down to 0.6A which is still a lot. As the issue started with the alarm randomly going off, I mostly want to know if I can just unplug the siren without creating issues so I can rule that out. I already looped the hood sensor a year ago so that isn't the problem this time.

 

SWAG here, perhaps the trunk hinge wiring is fatiguing through, causing erroneous boot-open state?

 

There is a feature called LAST ALARM ACTIVATION in the SETUP AND CONFIGURATION tab of the diagnostic WDS/IDS.

I can't remember what cars use this capability but I am pretty sure the X308 does.

The data logged in the modules will indicate what area to look for the fault. (what triggered the alarm)

That will be the fastest way to find the culprit.
Trial and error will be the only other alternative.

 

You could sit very quietly in the car & not move with the alarm set until it goes off & see if anything happened at the time.

A mate had to do that years ago as his alarm was going off about 2am every morning. He found a spider coming out the dash & crawling over the interior sensor on the windscreen pillar was triggering it. After the spider was evicted his neighbours got a lot happier.

 

There is a history of the alarm sounder battery failing ( shorting out internally ) from reading so a easy try to just remove plug

But since you asked ..........................

On ignition key removal, there is a linier switch in the key barrel with pins 4 and 5 making at the IG switch connector

This pin 4 is to the Security Lock Control Module that starts a lock down sequence ( the 20 seconds Motorcarman mentions )

this is also the seat / collum retract to exit command so that is a verification of pin 4 to 5 making

After all the position agreement are met ( seat exit position sensor reading, collum exit position sensor reading , locks in lock position sensors ) the SLCU will go to sleep drawing very little current like 20 milliamps

If the SLCU does not go to steep it will stay active and drain the battery in the form of a often called parasitic drain , a paricitic drain can also come from outside the alarm system but is a reference term that has stuck to the SLCU

You can take the large knob on the left side of the steering collum from auto to off and this removes the seats and steering collum from the equastion or variable of consideration

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The key barrel can be changed without a new key needed in worst case but not needed to remove switch attached to barrel for test , the key barrel can be lubed with graphite spray but a dripping mess on legs