Quote:
Originally Posted by scottmcphee
You can do this faster and cheaper on a w124. I bought a 2-channel momentary output remote pair and installed the receiver in my trunk. Tapped into the three wires going to the trunk latch, to get + and - for the receiver power, and one line controls lock and unlock. Grounding the wire (via output relay) locks, and providing a +12 to the wire (via the other output relay) unlocks. (I may have confused which is which.. but you get the idea).
Key still works everywhere as it should.
Don't care about the alarm since I've disconnected that, but I imagine this mod would work just fine. It emulates un/locking the whole vehicle from the trunk using a key. So if this key action would normally un/arm the factory alarm, then this model probably does the same using remote.
I haven't used a key in the door tumbler since...
The remote even has a lock / unlock symbols and is keychain style, and get this.. has metal and a slider cover... it's meant for vehicle application you can tell.
ebay... $10 GO CHINA!
working strong 2 years later
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More on this method...
Here are the wires to go after in the car trunk near the latch (1987 300D)
Red/White or maybe just Red is HOT +12 all the time, from battery.
Brown/Blk or maybe just Brown is GROUND all the time.
Yellow is the input to the computer.
Supply a +12 pulse on yellow (taken from the red wire is fine) for UNLOCK all doors.
Supply a GROUND pulse on yellow (taken from Brown wire is fine) for LOCK all doors.
I discovered something freshly after playing with these wires when doing the install. The car computer may ignore inputs on Yellow after the installation, hence the remote will appear to be not working. Stays this way until some event happened that caused the computer to reset. I think using the door lock with key to do a lock/unlock cycle, or starting the car, or something... forget exactly what, but it was simple and caused the car computer to begin paying attention to the remote signals again.
After doing that, supplying the pulses on the Yellow wire again at the trunk are revived.
I'd suggest trying to supply brief pulses on the Yellow wire MANUALLY by touching it for half second to the mentioned supply +12 or GROUND. When that's working, wire up your remote receiver relay to give these pulses when using the remote button.
When you release the button make sure the remote receiver is releasing the relay so the pulse comes off the Yellow wire so it is allowed to hang "free" again. Some remote receivers have a "latching" feature, don't pick that, use the "momemtary" feature... in other words the relay only holds for as long as you are holding the remote button.
The EMT diagram shows the Yellow input "resting" on +12 (Unlock). That's just a convention for diagramming, don't actually do that. Let Yellow hang free when neither remote button is being pressed, offering no signal to the computer. In order for you do this, you need a 2-channel remote, with 2 relays. If you try to use a 1-channel remote with 1 relay and just take off from its N.O. and N.C. contacts you won't be successful. (That was my first try).