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Cheap aftermarket RF locking

Discussion in 'Electrics, Vacuum, Ignition and ECU' started by alexanderfoti, Mar 27, 2017.

  1. alexanderfoti

    alexanderfoti MBO Forum Supporter Authorised Forum Supporter

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    It is common that the rear antenna amplifier fails on the C203. Its a window out job, and I am trying cheap fixes on this car.

    The IR door locking works now, (see other post), but it is still a pain. On to plan b.

    I purchased a cheap car remote control lock from ebay China (£7.99!!!) Link, Its basically a remote control relay with "rolling code functionality". Its likely very easy to bypass etc, but I do not leave anything of value inside the car.

    [​IMG]

    Its wiring diagram looks like this:

    [​IMG]



    Its basically 2 SPDT relays connected actuated by a remote control (with some other wires that flash lights and put windows up, if required).

    Early Mercedes have an odd quirk in that their interior unlock buttons work all the time (key off, car locked or unlocked). The idea here is to wire the output of this unit to the interior lock/unlock button so that the car can be locked/unlocked remotely.

    To start, we must remove the upper control panel:

    [​IMG]Then remove the silver screws:

    [​IMG]

    Then remove the buttons (the unclip as one unit) and remove the circuit board:

    [​IMG]

    After some nice probing with a mutltimeter it was decided that the buttons shared a negative ground, and had separate switched outputs.

    The idea then, is to tie together the COM outputs on the RF module, and connect them to this shared ground, and then the lock/unlock wires to the other side of each of the switches.

    To do this, we solder some wires to the relevant pads:

    [​IMG]



    And hot glue them in place:

    [​IMG]

    Note down which wire is which, then re-assemble:

    [​IMG] [​IMG]

    Off to the CAR!!!

    The control box requires constant 12V and Ground, easily obtained on the radio loom:





    [​IMG]

    The other cables connect to the cables we soldered to the buttons, COM to Blue cable, then lock/unlock to the red/black cables.

    The shove the whole lot behind the radio in the foam:

    [​IMG]

    Put all the fascia panels back in etc, and you now have a functioning remote control for £7.99.

    Original post here
     
    fellyman007 likes this.
  2. turbopete

    turbopete Senior Member

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    this set up reminds me of the remote locking add ons you could buy to link to aftermarket car alarms in the late 80s/and 90s

    good to see the issue can be solved cheaply (for once)
     
  3. OP
    alexanderfoti

    alexanderfoti MBO Forum Supporter Authorised Forum Supporter

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    It is nice to have a cheap fix for once!
     
  4. LostKiwi

    LostKiwi Senior Member

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    In theory you could also use one of these as a remote immobiliser. Just connect it to a hidden relay that controls the fuel pump and job done.
     
  5. Arzaam

    Arzaam Senior Member

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    i have the same issue on my w203, havent done the proper fix yet, this method looks better but seems intimidating, can you still get a 12v live and ground connection if you have the factory radio on the car like mine has? interestingly enough i get excellent radio reception so the dealer is puzzled and says to use the Ir as is as they are not sure if its the amplifier in the window. though it also unlocks if i hold the key 1 feet from the rear window.
     
    Last edited: Mar 29, 2017
  6. turbopete

    turbopete Senior Member

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    all the wires are there as I think the radio shown uses the stock MB wiring (possibly using a harness adaptor) and the MB radio still needs the ignition 12v feed, permanent 12v feed and an earth to make it work
     
  7. Naraic

    Naraic Moderator

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  8. OP
    alexanderfoti

    alexanderfoti MBO Forum Supporter Authorised Forum Supporter

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    This one is the same, Radio is absolutely fine, just the RF for the remote seems to be affected. I suspect its a particular section of the antenna amp that fails.

    I fixed the IR locking on the drivers door handle before, but its still inconvenient.

    Yes, this car uses an adaptor so the constant 12v wire is still there on the factory connector
     
  9. silestanix

    silestanix Senior Member

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    See I'm looking at my W202 Alex and thinking, could this also be done to a W202...? Convenience...?
     
  10. OP
    alexanderfoti

    alexanderfoti MBO Forum Supporter Authorised Forum Supporter

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    Should be doable. All you need to do is see if the dash lock buttons works with the key out.
     
  11. silestanix

    silestanix Senior Member

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    Mornin Alex, tried this last night and mine does indeed work, also left the window open, locked the car and reached in to press the button and still works too, result...
     
  12. OP
    alexanderfoti

    alexanderfoti MBO Forum Supporter Authorised Forum Supporter

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    Exactly what I did to test it too :)
     
  13. silestanix

    silestanix Senior Member

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    Ha, had to be done, pity about the alarm going off though but hey... Cheers for this btw, neat idea man!
     
  14. fellyman007

    fellyman007 New Registration

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    excellent no more getting soaked running to the car in the rain to unlock it , fantastic idea alexanderfoti. thank you
     
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