Looking for W126 factory alarm info. - PeachParts Mercedes-Benz Forum

SD Blue · #1 07-09-2008, 12:06 PM

Recently, I reconnected the factory alarm (disconn. by PO) and it worked fine for nearly 4 months. Then one evening, in a Texas downpour, it decided to not shut off with the door key so I disconnected it until I had enough time to sort out the problem.

However, I discovered that I could no longer get into my trunk. And after some searching on the forum, found out that there may be a locking solenoid that was activated by the alarm system. I haven't tried it yet, but hope that I can get the key switch to deactivate the alarm after reconnecting. From what I've read, the door locks can eventually cause the alarm to become temperamental. Is this something that can be cleaned, lubed or otherwise repaired or am I looking at replacing the door lock?

Does anyone have a schematic of the alarm system for the W126? (I don't currently have a copy of the FSM as it seems only available by download and I haven't sorted out how to do it with dial-up and this old computer.)

My ultimate goal is to have the factory alarm functional. But at the moment, I just need to be able to get in my trunk.

hangit · #2 07-09-2008, 12:39 PM

Here are the DIY links. Hope they help.

http://www.peachparts.com/shopforum/diesel-discussion/150748-factory-alarm-system-issues.html#post1143583.

John

bustedbenz · #3 07-09-2008, 01:35 PM

Quote:

Originally Posted by SD Blue

Recently, I reconnected the factory alarm (disconn. by PO) and it worked fine for nearly 4 months. Then one evening, in a Texas downpour, it decided to not shut off with the door key so I disconnected it until I had enough time to sort out the problem.

However, I discovered that I could no longer get into my trunk. And after some searching on the forum, found out that there may be a locking solenoid that was activated by the alarm system. I haven't tried it yet, but hope that I can get the key switch to deactivate the alarm after reconnecting. From what I've read, the door locks can eventually cause the alarm to become temperamental. Is this something that can be cleaned, lubed or otherwise repaired or am I looking at replacing the door lock?

Does anyone have a schematic of the alarm system for the W126? (I don't currently have a copy of the FSM as it seems only available by download and I haven't sorted out how to do it with dial-up and this old computer.)

My ultimate goal is to have the factory alarm functional. But at the moment, I just need to be able to get in my trunk.

I don't deny its existence but I'm not familiar with the alarm locking the trunk. Try unlocking it with your key one more time just to be sure you didn't lock it and forget it. Unlock at the trunk lock, I mean.

I left mine disconnected and haven't looked back. False alarms are too embarrassing, esp. in a university parking lot where you already are under suspicion.

pmckechnie · #4 07-09-2008, 06:14 PM

I had this problem with my 84 500SEL and I believe the SD is the same. When the doors are locked with the key, the alarm system locks the trunk with an electrical lock. The only way to get the trunk open is for the alarm system to unlock it. What you can try is to reconnect the alarm system, then unlock the doors with the key. Try both front doors. When you get it unlocked, disconnect the alarm system and it won't lock again this way. If this doesn't work, let me know and I will try to dig up a wiring diagram for the system.
Paul

SD Blue · #5 07-09-2008, 09:53 PM

I've been through all of the DIY links as this is how I found out about the alarm locking the trunk.

Well, I tried reconnecting the alarm and unlocking. The alarm didn't sound.

From the driver's door: All of the doors unlock but the trunk still remains locked. The key turns but the release button only depresses a little and doesn't unlatch.

From the passenger's door: I can't get anything to happen. That door only unlocks with no activation of the vacuum pump for the rest of the locks and the trunk remains locked.

If I had a copy of the schematic, I could certainly sort it out but currently I'm stuck with a locked trunk.

babymog · #6 07-09-2008, 10:00 PM

There is a secondary lock pin system that my '91 had, not sure whether it is activated by the central locking or otherwise.

pmckechnie · #7 07-10-2008, 07:21 AM

I'll check for diagrams when I get to work today. If I can't find it for the SD, I will send the diagrams for the 84 500SEL.
Paul

hangit · #8 07-10-2008, 09:19 AM

PM me your email address. I have the FSM schematics for your alarm system and I'll attempt to send you the PDF file.

John

pmckechnie · #9 07-10-2008, 11:41 AM

SD Blue, I could not find the diagrams but I found a alldata tsb that should help you out for now. It is a .txt document, atached below. Let me know if you can't open it. I will probably do something wrong.
Paul

SD Blue · #10 07-10-2008, 01:03 PM

Thanks Paul........

I will see if I can find the emergency trunk release cable mentioned and see if I can get it to release that way.

BTW, I noticed something strange last night while trying the door locks. After reconnecting the alarm and opening the driver's door, I heard a clicking inside the car (similar to the frequency of the horn when the alarm goes off). I connected a battery charger and let it charge overnight, hoping that may change things. Maybe a low battery is the source of the problem??? (I have read several reports here of alarms going off on their own and this may certainly be the cause. It may be a design flaw internal to the alarm unit.)