Commando 520-S error on Merc190E

I have installed the alarm/keyless entry on our 1991 Mercedes 190E 2.3 w/o factory alarm. There appeared to be no pre-existing alarm harness, and the wiring colors I have found are not 100% consistent with the database on this site.

The keyless entry works properly. I am getting an error signal on 'arm' - three beeps after the one indicating armed. The LED blinks slowly when armed - no error code - and is off when disarmed, steady on in valet mode. The programming modes appear to act normally. The only non-default condition I have set is the 3-sec lock/unlock timer.

The alarm will sound if any of the doors are opened, but not if the 'instant alarm' circuit is triggered - trunk or glove box. There is also no alarm from the shock sensor. After alarm, the unit does not reset properly until I put it in valet mode and back out.

The common rear door pin switch wire is connected by diode to the alarm (-) door trigger input. The front passenger door switch is connected by diode to the same place. The driver's door switch is not connected to any of the others or to the alarm, but it will trigger the alarm. I have no diagram explaining how it is wired into the delayed dome light unit. I cannot find a wire from it at that location, though I do find the one from the passenger's door.

I ran a wire forward from the trunk light switch, through a diode to the 'instant (-)' trigger on the alarm. Another connection through a diode to that point from the glove box light switch (and eventually another from the hood).

Is there any reason an error that might exist in the door switch circuit could cause no alarm in other trigger inputs - and yet still alarm on a door trigger? Does anyone know the wiring of this vehicle's front dome light/doorswitch circuit? Thanks for any help.

Steve

I installed a 520-S on my Miata over the weekend.  In testing, I noticed that if, I armed it with the hood up - I get the 'defective sensor reminder' signal as expected, and the shock sensor (and the proximity sensor which is connected through diodes to the shock sensor inputs) will not trigger the alarm.  It seems that perhaps the 520-S is programmed to ignore these inputs if it is armed with a open sensor?

In any case, it sounds as if one of your door, trunk, or hood connections is still showing open to the alarm even when closed.  Have you tried to verify with a DMM that these triggers are functioning as you expect them to?

The alarm triggered indicators should reset just by turning the ignition to 'on'.

Hope that helps at least a little.

Chris

Thanks for the input guys, this give me something to work on.

2vmodular, the doors do actually set off the alarm when opened, but I will check out the buzzer location as a trigger. The rear doors have a simple circuit and I am certain that is not a problem, but the front is more complicated.

Chris, it is good to know your unit is behaving like mine in some respects - helps decide what is normal behavior and what isn't. I have checked all lines with a dmm, and everything seems as expected - but the front door pin wiring is a mystery in this Mercedes. I think my next move will be to disconnect the front door switches from the alarm and see if it behaves normally without this. If so, then I may have to get inventive, or try 2vmodular's point of tap-in.

Steve

A post-op follow-up. I found my problem - the error was in the 'instant trigger' zone of my wiring. I had used the glove-box light switch as a trigger on that zone, along with the trunk light switch. I was fooled because everything seemed to work fine when the glovebox lamp fixture was unplugged, including triggering on the glovebox door. With everything reassembled and the lamp plugged in -error and zone deactivated.

The problem is the circuit the lamp uses has ignition switched 12V, and it is very noisy from something else on that circuit when the ignition is off. I decided not to use that as a trigger, and everything works fine now. I kept my front door trigger where it was, which is triggered by the passenger's door. Through some obscure wiring path, it triggers on the driver's door as well with no errors. As far as the shock sensor, violently shaking the car had no effect, but a light rap on the window beeped the alarm - so I guess it's fine.

One thing I had added was a return through a diode from the KE unlock pulse line to the door trigger circuit - to trigger 'on' the delayed dome light when unlock/disarm pressed. This did not contribute to my problem, but disabled the auto-relock/rearm function of the alarm. I disconnected this mod, as this is a nicer feature than the dome light trigger. I could reactivate it using a relay if I want to dig harder into the vehicle wiring - but not for now.

Thanks to those that responded, and to this site in general for a lot of insight into a field I plunged into knowing nothing other than general electronics.

Steve