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  #1  
Old 06-10-2019, 03:18 PM
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Location: Seattle
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what is this grounded metal bracket by my stereo (early w124)

P/O removed the original becker from my 1987 300TD and never added another radio. I'm trying to sort out the wiring so I can install a new radio. Most of it is straight forward, but there is this loose metal bracket the looks to have a ground attached to it that I'm not sure what it is (red circle in photo). Is this part of the original becker theft protection? Or something else?

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  #2  
Old 06-10-2019, 04:31 PM
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Location: Columbia, SC
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Yes that was the alarm trigger wire. It was meant to be plugged loosely into the radio and get grounded by the radio frame. The idea was that if a thug pulled out the radio, the strap fell off, ground got broken, and the vehicle alarm sounded.

The slightly later ones had a 5 pin (latching) plug in the back. If you pulled out that plug the wrong way (with battery but no ignition IIRC) it would activate a self destruct that nuked the radio electronics in addition to setting off the alarm. There was a Mercury battery (the forerunner to the Lithium cells we all know for memory backup) that provided the energy to operate this death circuit. I seem to recall that if you send one of these into Becker for a rebuild they disable this circuit and remove the mercury battery since it is long dead by now.

And that single tail (blue wire/black sheath) with the quick connect is your power antenna trigger wire. This will tie into and work with the blue wire on a modern stereo. If you got a more upscale stereo it may have 2 blue wires, one for amplifier activation (on anytime the unit is on) and another for power antenna (on only when radio is selected).
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The OM 642/722.9 powered family
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)
2008 ML320 CDI (Older sonís DD)
2008 E320 Bluetec (Younger son's DD)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech
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Old 06-10-2019, 04:51 PM
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Thanks for confirming.

Interestingly the radio, which I think was a 754 model, had a spot in the middle for a five pin plug (Similar to the 780 model shown here Becker Grand Prix Electronic Model BE 780). In fact I'm pretty sure the plug you can see in the picture at the lower left corner is the five pin plug. So maybe the 754 had both?

I'm assuming I could remove the metal piece and tape off the connect.
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