1986 W126 Security System Operation - Radio “Trigger” Circuit
 

Hello all,

A quick question about the function of the security system on a 1986 560SEL as it pertains to the factory Becker 754 installation and the 5-pin security connector that is also spliced into that spring-clip “trigger” -

Namely does the security system activate when ground is broken or does it activate when ground is established upon radio removal?

For example - when installing an aftermarket HU should one ground the security wire or, instead, make damn sure one doesn't?

I am certain that at some earlier point in my car's life when the security system for the radio was unplugged that the 5-pin security wire WAS grounded meaning that that is either 1) good practice or 2) that my security system has some deeper issues – i.e. not recognizing radio removal.

Right now I have it grounded w/o the alarm going off.

Thanks in advance!

As I understand it that connection can be left disconnected. It is grounded when the alarm is armed, and if the radio's power is removed while that connection is grounded the radio disabled itself.

-J

Thanks a millon.

The logic of the what and the how of the security system as it relates to the factory radio is something that has eluded me for some time now. That 5-pins are seemingly required for a simple on/off, yes/no function doesn't help to make it terribly clear as to what is going on...

Cheers!

Just one of those wires goes to the alarm - I think brown?

And yes it should be connected to the metal case [ground] of the new radio if you want that protected by the alarm - activates with loss of the ground connection.

You can test this by rolling down a window, locking the car, then reaching in through the window to disconnect (unground) that wire. The alarm arms when the doors are locked.

Hmmm...

Now you have me almost convinced that my security system is well and truely buggered - I had been driving around un-radioded and un-grounded for two weeks and not a peep out of it...

Actually it is a *very* forgiving alarm system. You can leave the radio alarm wire ungrounded and the alarm system will still arm and the other sensors will work.

With the radio wire disconnected, lock the car door with the key, then reach in and open the car door using the handle. The alarm should sound.

Good to know...
 

I'll be sure to remember that *very* the next time it has a nervous breakdown leaving me to pull fuses in the pouring rain in a Quick-E-Mart parking lot at 3:19 AM to the sweet sound of its melodious braying...

:D

Seriously though, VERY MANY thanks for clearing that one up.

Cheers!