the other day my 09 f150 rear lower left door ajar light came on I've sprayed WD 40 contact cleaner check the fuses I've disconnected the battery still with no luck anyone out there got ideas

 

I'm having the same problem and tried the same things you did. I've been searching other solutions and it looks like owners have tried various things to rectify the problem. My next step is to check the wiring in the accordion type sleeve between the door and the body. Some owners have reported the wires being pinched. When I first noticed the problem, it was as if it had a short because mines would go out and then come back on again. It did that on three separate occasions before it finally stayed on and now it won't go out at all. So that's my next step. Please let me know what you try/discover.

 

Ok so I have had a real problem with my 2013 F150 I haven had a an f150 in 9 years I've finally got myself into a position to buy one and I'm having some minor problems. Two day after I bought it the left rear door lock wouldn't unlock so I looked at the wording harness inbetween the door and found the bigger gauge wire and the gray and red wire where broke so I pulled the door apart and pulled out the harness and repaired the broken wires once I put it all back together the door would unlock but wouldn't lock. So I pulled the back seat and the drivers seat out folded up the carpet and found they the gray and red wire was melted all the way across the back and up to the dash most of the way a long it has Baird itself and melted itself to the solid green wire. I'm not sure why a fuse didn't blow and I'm very lucky in my truck didn't catch on fire. So I replaced the gray and red wire along with the green wire once I put it back together The doorlock started working however it was saying that that door was ajar on the dash and my domelight's will stay on for 10 minutes after getting out of the truck so I bought a new doorlatch thinking that maybe the sensor had gone bad because those wires were melted together upon installing the new door latchi'm still having the same problem the light on the dash tells me the left rear door is ajar please help I'm going crazy

 

Here is the part number to fix the door ajar issue, they are back ordered right now.

AL3Z-14630-AAA