Hi Randy,

I think you're doing pretty good with that wiring diagram. Your test results at the driver door are fine. The driver door lock switch shouldn't be a problem as your yellow-black wire test (forcing the relay to do a lock) made no difference. You say you've got a good relay and the 12 volts you saw at the blue-red wire would seem to verify that.

If the actuator motors are making an effort to lock (you hear a hum) then they're getting power (+12 volts at all their blue-red wires during a lock). That leaves me to wonder if they're either all physically frozen (I doubt it) or perhaps one actuator isn't working and is sucking so much current there isn't enough juice for the other actuator motors to do anything more than hum. I don't think just having one or more actuators simply jam up would cause this, although I can't swear to that. I think it would have to be one that has partially shorted windings (but not enough to take out the fuse). In any case, if one is drawing too much current and if you held the driver door lock down for a long time (or drove around with your elbow on it) then the relay could overheat and eventually fry (just like the original).

Based on that theory, I'd open each door/trunk panel, disconnect its actuator motor then re-test at the driver door until I found the one that's causing the problem. If one door lock is stiffer than the others or one door actuator motor hums less than the others then start there. Leave each actuator disconnected as you go in case you have multiple problems. Make sure the button, linkage rod, actuator and locking mechanism operate freely -bend/lubricate as needed. Look for any evidence of a jimmy bar being used.

You can try using your meter to check resistance through the windings of each one just as you did at the driver door. I can't tell you the normal range of ohms, but somewhere around that .23 ohm resistance would seem about right. Obviously zero ohms means a total short (that would cause a blown fuse) and infinite resistance means an open circuit (which shouldn't affect the other actuators or the relay). So you're looking for one that has abnormally low resistance. All the actuators are basically the same except for the trunk/tail gate, so don't get too excited if it's a bit different.

I think the later 740 actuators are the same as the 900's -at least the call-out pictures in the 1989 740 green manual wiring diagrams are the same. If you're lucky the early 740 actuators just have a different shape so you may be able to cannibalize the guts out of one. I can't remember if they can be easily opened up or if you have to destroy them to get inside.

Huh, I just noticed in the wiring diagram that my wagon tailgate lock has a cut-out switch. Is that where I have to hold the key in the lock then stand on my head without turning the key? I obviously don't use that feature very often.
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Dave -940's, prev 740/240/140/120 You'd think I'd have learned by now