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Trying to diagnose door ajar sensors via GEM connector

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Hello --

I have an '01 Mercury Sable LS sedan, and the interior dome lights won't go out, I had to pull the fuse to get them to go off.  So I'm suspecting a problem with one of the door ajar sensors.

Looking through the wiring diagrams, I found connector C201c which attaches directly to the GEM, and has a ground pin and also a door ajar pin for each of the four doors.  So I had the idea to pull off this connector and test for continuity between ground and each of the four pins to see which sensors are showing the doors open. 

When I took off the connector, I found all the wires seem to be in the positions and have the colors as shown in the wiring chart, except that the black ground wire was missing!  So I hooked a wire to a nearby ground point and tried the test, but couldn't find any continuity between any of the door ajar pins and ground, with the doors either open or closed.  So now I'm completely stumped.

So my questions are: Is this a valid diagnostic test for the door ajar sensors?  If so, what am I doing wrong?  Is the absence of the ground wire in the connector a problem?  The GEM is grounded via a different connector (according to the wiring diagrams) so maybe it's not an issue, but it seems like the ground wire should be there in C201c.

Thanks for any advice,


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  • 4 weeks later...

Common issue, I had this with my '03 Sable this week. The "battery saver" should shut the lights off after several minutes. Still have a door switch but need to know which door. When the BS shuts the lights off, open one door and if the interior lights come back on, that door is good. Have to let it rest till the BS shuts the light off. Try a different door. If the door switch is stuck, it will not trigger the BS to re-light the interior. My case was the hatch on the wagon. I will likely pull the trim and disconnect the switch. 


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