As I'm sure the moderator knows by now, I like to tinker, plan, build, and generally screw my car up. Here is a brief overview of my much-more-complicated-than-it-needs-to-be keyless entry plans. If you have suggestions, comments, advice, or a jet black 1990 760 Turbo you're willing to sell me for $500, please feel free to respond.

I have already fitted my driver side door with a lock motor and associated linkages from my 1986 740, lovingly known by family and freinds as "That blue peice of".

I am currently exploring my options for adding keyless entry to my 1989 760. The car has almost every feature available that year, which means I'll have to add wires across the hinge. This is unacceptable. After reviewing the wiring to the lock position sensor, I discovered that all three wires (that includes the independant ground) run across the hinge.

My plan involves using the sensor ground wire and a pair of relays on either side of the hinge, a master and a slave. The master (dash side) relay is energized by the receiver changing the lock position; which switches the ground wire from GND to BATT, and the UP/DOWN wires to their respective motor control lines. The slave relay is energized by the +12v on ground and does the same switch door side. This allows the control of the driver lock motor without additional cross-hinge wiring.

Assuming you are coveting your central locking, there is a catch. The catch is that when the switch is reconnected to the central locking relay, the remaining doors follow the leader. Since most systems take a second depress to unlock the passenger doors, this is not the desired effect.

After breif testing, I discovered that the central locking relay does not fire on power up. I plan on exploiting this. A pair of diodes will convert UP/DOWN to a "Door Movement" signal that triggers a monostable 555 timer, which opens a relay cutting power to the central locking relay.

The 740 has extra wiring between the dash and the door for optional items such as power mirrors and... uh... some other stuff I'm sure. I'd also bet a pack of ramen the 940 has simmilar artifacts. Either way, the wire multiplexing circuit is not as valuable to the 9/740 owner as the CL inhibit timer.

Hopefully this URL-to-pic thing works like I think it will. I currently do not have values for R1 and C1 as those fix the delay, which all depends on the receiver.

By the way, I have a key fob from a 2001 series. Anyone know where I can find a compatible receiver? Thanks.
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89 764 GLE 150k/ 86 745 GLE 240k