The central locking system in my 86 740T stopped working last week. I can mechanically lock the car one door at a time with the knob or key, but using the key to lock/unlock all doors from the driver door is impossible.
I have spent several hours over several days tracing wires and trying to figure out what is wrong. Here is what I have discovered:
- The fuse is good (#2 in the rack)
-The relay SEEMS good; this relay is "K", and also powers the flasher on the stalk. I did try a "K" unit from another car with no success. The flasher works, which makes me think the relay is good.
-there are three wires going to the lock in the drivers door. One green with black tracer, one yellow with black tracer, and one black ground wire. There is no current apparent in any wire. The black wire is grounded well (ohmeter)
-I traced the green/black and yellow/black through the door hinge and under the dash to a major cylindrical junction with about twenty wires. There is no power in these two wires at either side of the junction. This confirmed that there the problem is not at the door hinge as I had expected, but must exist is further upstream.
- I was unable to trace the wires from the junction block to the relay due to its route high up under the dash.
-I removed the passenger door, and found that the three wires powering the passenger door have unswitched power through two of them and the thrid is a good ground wire.
-another thing I discovered is that I cannot seem to follow the schematic in the Haynes manual (surprise surprise).

Is there supposed to be unswitched current in both the green/black and yellow black wires in the drivers' door?
Do both of these wires go right to the relay?
Or is there another junction between the relay and the cylindrical block I described?
Can anyone provide me with a good description of where the various wires for this mechanism go? (i.e. is able to decipher the Haynes heiroglyphics)
Are these doors wired so that if there is a break in one of the wires in the doors, or the trunk, they all crap out?
Is there some way to test the driver lock mechanism via application of 12V power without frying something?

Any help or advice or relating of similar experience with solution would be vastly appreciated; this is driving me nuts. I think I can remove and reinstall door panels with my eyes closed now.

JD
65 1800S
84 240GLE
86 740T
87 740T (donor car)
88 740T
92 960GLE