good afternoon and thank you for choosing JustAnswer. First i would like you to double check your dimmer switch and make sure it is not fully turned up as this will illuminate the runningboard as well as interior courtesy lights. If the dimmer is not the cause, then most likely the cause of this is a sticking or seized door ajar switch which would keep the lights on thinking one of the doors is open. To attempt to resolve this you can purchase a can of PB Blaster and liberally spray each door latch,then slam each door about 10-15 times ,then respray the latches and reslam the doors again another 10 times. This might work to free up the switch if it isn't too badly seized, if this doesn't resolve the concern then you will need to replace the ajar switch. To determine which switch is at fault the use of the Ford scantool will be required , or you can replace the driver's ajar switch and see if this corrects it, as usually in most cases it is the driver's door switch that seizes up as it is the door that is mostly used. If you prefer to identify the switch at fault before replacing a switch, you can have the dealer hook up the scantool and they will advise you which switch is falsely reading ajar, they will likely charge you $45 for this though some dealers will do this free of charge,...if asked nicely of course
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