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1970 Mark III Courtesy Light Issue

Hi Bill,

You have helped me out before. So my driver door courtesy light does not work. Tested bulb works with a battery hooked up to it. all interior courtesy lights dash, map and reading lights work. I hear the solenoid seat release work when I open door also all lights work when opening both doors except the driver door. I tested for power and the plug at the door armrest I took off the armrest unplugged light switch and tested for power but nothing. So my question where do I start at the door jam switch?


Hi Phil –

From your description, it sounds like all of the lights and switches are working correctly except for the driver’s door courtesy light. You have tested this bulb and found that it works o/k when it was tested. If the above is correct and there is no power to the socket and the bulbs ground circuit is o/k, I would then believe that power is not getting to this bulb socket as it is to the other courtesy light bulbs. I would then test the left front door light wiring circuit with the aid of the “proper wiring diagram” from where it joins the other bulbs power supply and travels to and through the left front door jamb wiring harness and then to the left front door socket in the door for that light.  You will be looking for and correcting an open circuit etc. or any other reason for no power not being fed to that socket. We hope that the above information helps you. Let us know what you find.




Bill –

Thank you for a quick response. I will let you know what I find. question on the door jam plungers is one of them a master meaning one jumps power to the other? I have the manual i will look that up. Are all inside courtesy lights in series? and driver door being the last run on the list? just trying to get to a obvious prognosis before diving in every location.



Phil –

Your wiring diagram will answer your latest questions. The bulb socket in the left door should be receiving power from the fuse box at all times from a green wire with a yellow stripe. From there the black wire with a blue stripe leads out to be grounded in order to turn the bulb on if a door is opened or another courtesy light switch is operated etc. This wiring can be complicated and can require strong concentration while reading the diagrams. This is why a correct vehicle wiring diagram is a must in order to properly and clearly answer those questions as you are diagnosing. We may still have some available at Lincoln Land if you do not have one.



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