R129 Alarm issues

[B7TMW]

Hi. My 1998 V6 R129, has an issue with the alarm that I am seriously struggling with. This is (I believe) the dealer fit Scorpion system that was also fitted in a few other models during this period. I am looking for an installation diagram and a user manual for it due to the following. Can anyone supply????

Below is my problem;

It all works exactly as it should to a point. I have 3 remote keys with the car, all lock and unlock, indicators flash accordingly. I have the two alarm emergency fobs, one red one black and the port for these is present in the drivers footwell. It arms via the remote keys and triggers via the movement sensors or opening of doors bonnet or boot. Indicators all flash accordingly again until it re arms itself.

HOWEVER: it is silent. No siren sound at all.

I took the original siren assembly out and got into it. The PCB was shot to bits and the back up batteries had leaked.

Sirens are no longer available from Mercedes. I had a long conversation with the parts guy in Crawley (very helpful) who spoke to a long standing technician who was the one that tipped me off with the Scorpion name.

So I sourced a 2nd hand replacement siren assembly, with the correct plug etc. from a well known R129 place. First thing I did was open it and the PCB is immaculate. Back up batteries however were only reading 5V instead of the proper 7.2V. I plugged it into the car and it struggled but worked. I thought I'd cracked it. So ordered a new set of 7.2V back up batteries on line. Plugged them in and thought nothing more of it. Came back from holiday and the original problem had returned. NO sound.

Got back inside the siren to find the new batteries at 0.0V. Then I checked further. The polarity of the new battery was reversed in the plug!
I took the PCB to a PCB repair guy who checked it and reckons it's all ok as there was a protection system in place to stop reverse voltage doing any damage. He did find a corroded joint to the speaker so remade that. Still no sound.

I purchased yet another set of 7.2V batteries and this time the polarity is correct.

I then sourced another Siren and on receiving that, opened it and again, a perfect clean PCB. Put the new batteries in that (and the first one purchased) and again, NO SOUND from either of the purchased units.

I'm stumped. I have what appear to be 2 good, undamaged sirens, a good set of 7.2V batteries with the correct plug formation and I cannot get a peep out of it.

Could it be in silent mode? Is there a silent / valet mode? Where is the main brain for it?

I have no instruction for operation and I have no instructions for installation. I'm just spending money, stabbing in the dark.

Can anyone assist with instructions or wiring diagrams so I can continue to diagnose it?

Has anyone purchased a different aftermarket siren to replace the original?

Many thanks in advance and I hope I have explained the issue clear enough.

P.S. I don't want another alarm fitted and an additional fob. The remote keys to the car all work fine and I strive for originality.

 

[Wearsafoxhat]

There is a module in the boot, above the vacuum pump and a fuse for this in the boot fuse box labelled ATA. This may have been removed if the alarm was playing up..

 

[B7TMW]

There is a module in the boot, above the vacuum pump and a fuse for this in the boot fuse box labelled ATA. This may have been removed if the alarm was playing up..

There is nothing above the Vacuum pump. Everything is located under the steering wheel.

What I have discovered is that when fitted, they didn’t fit the LED.

I have now connected the LED and the only thing it displays is two short flashes then nothing when arming / locking the car.

I believe it should show a solid light for 40 secs then flash when the initial arming period is over.

This suggests it’s in some sort of config or test mode. But no matter what I do, I cannot appear get it to arm properly. I’m thinking its in a test mode so will only flash the indicators and not operate the siren.

I now have access to some fitting instructions of sorts but it’s not corresponding exactly to what’s in the car.

As you can see, I am stabbing in the dark somewhat.

 

[Wearsafoxhat]

It appears that your Anti Theft Alarm module is not there, is there or was there a fuse for it….

 

[B7TMW]

It appears that your Anti Theft Alarm module is not there, is there or was there a fuse for it….

Unsure what year that is?

Mine is all under the dash. Fuses are all good. It’s all fused from the front end fuse box by the offside bonnet hinge. I tried everything yesterday but cannot get anything other than 2 flashes on the LED on arming either by the key or the emergency touch port using the emergency dongles.

It locks, it arms, trigger it and all the indicators flash. But thats it.

I have ordered what I think is a new old stock Scorpion for Mercedes Alarm Kit. All the part numbers are exactly the same as mine so will keep this post updated with any progress.

 

[Wearsafoxhat]

mine is a ‘98 too. do you have a fuse box in the boot ? ATA.. fuse No 5 in mine,
perhaps the alarm has been replaced or was an upgrade.

I have the module in the boot and the siren in the engine bay, no internal movement sensors…
not sure what else I can suggest atm, but will keep thinking.

 

[B7TMW]

mine is a ‘98 too. do you have a fuse box in the boot ? ATA.. fuse No 5 in mine,
perhaps the alarm has been replaced or was an upgrade.

I have the module in the boot and the siren in the engine bay, no internal movement sensors…
not sure what else I can suggest atm, but will keep thinking.

Yes. Fuse box in boot. All fuses are ok. It’s a dealer fitted alarm when it was new.

Scorpion developed bespoke systems for mercedes. They even came in a mercedes box.

As I said, the dealers tech knew exactly what system it is.