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Well my alarm started going off on its own today. The alarm didn't even have to be armed. About 8 times, 10 minutes apart, just sitting in my driveway. So I pulled in inner fender cover and unplugged the siren.
Here is a picture of the siren mounted in a metal shield. The red wire is going to it. That is the connector I unplugged.
I just joined third forum so this may be outdated info, but I just replaced my alarm siren which is the part you are referring to and I opened my old component and the batteries are located inside. Not sure if you can buy just the battery pack because the siren is a sealed unit. The replacement part was $200.
if your alarm siren is marked with this code (203 820 38 26), like in mine W208, the battery is inside the unit.
This unit can be opened by removing the two screws on the back and by patiently open it (it's possible that it was sealed with silicon, like mine).
Once opened, you can easly access the battery.
The battery is a 7,2V 140mAh composed by 6 Varta V150H elements in series.
I was unable to find the exact replacement with cable and connector, but it's quite simple to adapt a "standard" 6/V150H battery. You have just to solder the original cable on it, respecting the polarity.
Check if the circuit board was damaged by the battery acid. I had to wash the entire printed circuit board and rework some soldering in my unit.
I am about to change the alarm sounder on my W203. Does anyone know what size of Torx is required to remove the alarm. Am I right in thinking it is a security Torx?
Also - Should I disconnect the main car battery prior to installation of the alarm sounder? I have heard horror stories about things going wrong when the battery is disconnected.
Thanks
Stewart
Last edited by stewbacca3; 08-08-2014 at 11:18 AM.
* The bolt is T40 ... I drilled out the security pin so I could use a normal torx bit ... the metal for this screw is soft so it took only a few minutes to drill out the pin.
* I cut the housing apart using a Dremel with plastic cutting wheel ... kind of a mess ... a tabletop bandsaw would have done much better. Just cut around the opening and go in only 1/8" or else you will cut into the components inside.
* As you can see from the pics, the PC board is kind of a mess. I'm not sure it's worth the hassle at this point of spending $30-40 on new batteries, trying to clean that PC board, and then gluing the case back together so that it's intact and waterproof. But I at least thought I would pass these pics along in case someone else wants to attempt it.
Okay, this is a couple year old thread, but I just recently had this problem too. I used a hot plastic knife tool to open the one from my 2008 CLK350 convertible. I ordered the batteries on ebay, but while waiting for the batteries to get here, I accidentally knocked the bucket with my parts on the floor. The board went accross the floor. I knew that messed something up. Sure enough, after getting it put back together with the new batteries, it would chirp, chirp, chirp, chirp when I locked it with the key FOB. I looked that up and found it would be caused by water getting inside the alarm. So when it dropped on the floor, it damaged something to make it act up. So, I purchased a used one on ebay, figuring I will just put the new batteries on that one, figuring the batteries on the one I just got would be old and ready to do the same thing. So I ended up using the dremel tool to open it. That worked out nicely, but then I noticed the newer one doesn't even have the batteries in it. So I guess that means the newer cars don't have the battery backup, just in case someone disconnects the battery, to try to steal the car. It does have the spots to solder the batteries in. So I will put the new batteries on the new verson. Let me know if that's wrong, if it isn't recommended please. I don't see why it would be a problem.
Okay, this is a couple year old thread, but I just recently had this problem too. I used a hot plastic knife tool to open the one from my 2008 CLK350 convertible. I ordered the batteries on ebay, but while waiting for the batteries to get here, I accidentally knocked the bucket with my parts on the floor. The board went accross the floor. I knew that messed something up. Sure enough, after getting it put back together with the new batteries, it would chirp, chirp, chirp, chirp when I locked it with the key FOB. I looked that up and found it would be caused by water getting inside the alarm. So when it dropped on the floor, it damaged something to make it act up. So, I purchased a used one on ebay, figuring I will just put the new batteries on that one, figuring the batteries on the one I just got would be old and ready to do the same thing. So I ended up using the dremel tool to open it. That worked out nicely, but then I noticed the newer one doesn't even have the batteries in it. So I guess that means the newer cars don't have the battery backup, just in case someone disconnects the battery, to try to steal the car. It does have the spots to solder the batteries in. So I will put the new batteries on the new verson. Let me know if that's wrong, if it isn't recommended please. I don't see why it would be a problem.
what year vehicle/type did this new alarm come from? I'm in the process of replacing the batteries in my control board is horribly corroded.
02-19-2011, 07:48 PM
