I recently purchased an '88 300CE and have been trying to fix the most urgent issues.

One that has me stumped is the on board alarm system. Here's the story behind what's been happening.

A day or two after I had been driving the car (post purchase) I started the car and began to hear a "clicking" sound. The sound seemed to be coming from under the dash on the passenger side. The clicking sound had two separate speeds, one the same frequency of ticking as the turn signal and the other half a second slower between ticks. The sound would subside after a period of approximately 1-2 minutes (I haven't timed it specifically) and whenever the brake is depressed the clicking returns. I found out when I took it to the Mercedes dealership for a checkup that the clicking was the alarm system and that the only reason the horn and lights weren't going off was because the alarm had been "tampered with and disabled, and would probably have to be replaced" (Mercedes dealer).

I asked the man from whom I purchased the car if he had ever had problems with the alarm system before. He mentioned that a few years ago when he and his wife were driving home, the alarm system was constantly going off. He took it to the Mercedes dealer (the same I took it to) and they had no idea why it was going off, with no way of fixing it. He told them just to disable it if they couldn't figure out the issue. Odd that they told me that it had been tampered with. Of course, they didn't know it was the same car I suppose. They said the fix would be to replace all the key tumblers in the door and the ignition. I didn't see how that would help as his starter and tumblers had all been replaced at 100,000 miles. The car now has approximately 140,000 on it.

Confused and just looking for answers. Perhaps I can disable the fuse that is connected to the alarm system (or is that not even tied to a separate fuse.) The only other thing I can think of is to do what they say.

One last clue, perhaps because the previous owner's son had replaced the blaupunkt radio, which is tied into the security system, that has also been causing alarm issues?

Thanks for putting up with the long post. If you have questions because I really have no way to best describe my issue, please feel free to leave them and I'll check daily.

Thanks!

Cmarison

Is a bit confusing.
The car is currently making these clicking noises, and that's what you want to fix, or do you actually want to fix the alarm system so it works?
If the alarm constantly goes off, WHEN DRIVING, it's usually the control box. "Tampering" usually involves disconnecting the control box, which is kind of under the passengers feet, under a black plastic panel which is under the carpeting. I'd see if the box is disconnected if you want to solve the clicking. The radio work done should involve taping up the lead behind the radio, but if you disconnect the control box it won't be a concern, it will be a concern if you want the radio repaired.
The dealer has (or should have) a monitor device which they plug in in place of the control box which monitors all the inputs, this should tell them if they have a problem with any of the switches that trigger the system, if they all prove to be OK I would consider a new control box, although I'd rather study the diagnostic routine before commiting to that. What they are suggesting seems like a bit of a shotgun approach, how/why would all 3 of these parts go bad at once? If you are capable of removing the panel under the carpet under the passengers feet (easy job, just 1 screw i think) then the module you want I believe also has "Blaupunkt" on a label on it. 2 connectors, 1 input 1 output. Remove both.
Gilly

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Just unplug the alarm module as mentioned previously. I have done this on every MB I have owned (at least the ones that have had the module). The alarm is pretty useless anyway. Pretty funny, though, when it malfunctions - people will "pull-over" thinking you're a cop due to all the pretty flashing lights...

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Firstly I'd like to respond to gmercoleza, because I laughed when I read about the people pulling over thing. Great stuff.


To Gilly, your experience and advice is invaluable. I suppose the easiest thing to do would be to disable the control box. What was happening was that the horn and lights weren't going off, but the box I suppose was still sending the signal, hence the metronomical click click. So, I suppose I'll attempt disconnecting the control box until I can replace the control box.

I suppose what kinda urks me is that the dealership wanted to kill the mosquitto with the cannon. They didn't say that they could check the connections, all they said was that the whole system should be replaced. That i suppose gets them more money.

Cmarison

Question:
Was an alarm system standard in the 1988 300CE?

If so, I was totally unaware that I had/have one! Brother!
The previous owner must have disabled it!

BTW the original radio on mine was a Becker I think. (It's on a shelf in the garage.)

I had this problem intermittently with our CE last year.... it went away... but I think it is a tumbler issue on the front door.

If it ever comes back, I will un-hook the box.

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1989 300ce 129k
( facelifted front,updated tail lights, lowered suspension,bilstein sports, lorinser front spoiler, MOMO steering wheel, remus exhaust,stainless steel brake lines). (Gone)

1997 s320 154k (what a ride). Sold with 179k miles. Replaced with Hyundai Equus

1994 e320 Cabriolet 108k



1972 280se 4.5 153k Owned for 12 yrs, sorry I sold it


[/SIGPIC]

I just rebuilt one of my cars' driver side lock cylinders a couple weeks ago, so this is fresh in my head.

When you remove the door handle and subsequently the lock cylinder, you will notice a black plastic component that clips on and "wraps" around the cylinder - this is the alarm sensor. A green wire comes off this component, runs through the door, and ties in somehow with the security system. Interestingly, like I said the sensor just wraps around the cylinder but is not mechanically activated so I guess that means it is an inductive sensor. Knowing that puts things in perspective as it is very easy for this sensor to lose sensitivity with age and exposure to elements.

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08 W251 R350
97 W210 E320
91 W124 300E
86 W126 560SEL
85 W126 380SE Silver
85 W126 380SE Cranberry
79 W123 250
78 W123 280E
75 W114 280

Lee,

It could be a tumbler issue, however I've unlocked the doors using each lock (passenger, driver, and trunk) and each time the alarm will still trip. It is a good point about the tumbler, though with what gmercoleza said, it would be odd if all of them went bad in my situation. So perhaps with my specific incident it is the controler that has gone bad and not the tumbler?

gmercoleza,

About the green wire sensor, do you think I should also check that? Perhaps I will when I am ready (also money wise) to fix the issues without just disabling the control box.



I am about to go and disconnect the control box, wish me luck

Cmarison

I just posted my observations; I have no idea how to test the system, and frankly I have no interest either. For $100 you could put a good alarm system on the car, superior to the quirky one that's on there now. Of course it won't be original, but that's a tradeoff that has to be made sometimes.

I would do a search on this site; maybe someone who knows about these things has posted some information. I say just disconnect the sucker and be done with it. I've never looked back...

__________________
08 W251 R350
97 W210 E320
91 W124 300E
86 W126 560SEL
85 W126 380SE Silver
85 W126 380SE Cranberry
79 W123 250
78 W123 280E
75 W114 280