Door ajar light on and doors all closed then interior lights flashing on and off and then factory alarm going on and off

courtesy light switch , is door ajar switch an it's part of the door lock actuator . Light on coming on ? Not going off ? The ajar switch is a input to the GEM module , fords BCM - body control module . The GEM will energize a relay to turn on the lights .
The GEM will illuminate the interior lamps when any door is open or ajar. The interior lamps are; the dome lamp, the rear cargo lamp, the door courtesy lamp and the side rail lamps. The courtesy lamps will shut off when the doors are closed and the illuminated entry feature is not active or when the vehicle speed is greater than 5 mph (8 km/h). The interior lamps will not be reactivated until the vehicle speed is less than 3 mph (5 km/h) and a new door open warning lamp switch is received.
The GEM controls the interior lamps illuminated entry function by activating the interior lamp relay.
Mite be a good idea to have it check for DTC'S - diagnostic trouble codes .

B1322 Driver Door Ajar Circuit Short to Ground GEM GO to Pinpoint Test B . B1323 Door Ajar Lamp Circuit Failure GEM REFER to Section 413-01 . B1325 Door Ajar Lamp Circuit Short to Battery GEM REFER to Section 413-01 . B1330 Passenger Door Ajar Circuit Short to Ground GEM REFER to Section 417-02 . B1334 Decklid Ajar Rear Door Circuit Short to Ground GEM GO to Pinpoint Test C . B1338 Door Ajar RR Circuit Short to Ground

The door switch doesn't go to the dome lights , the switch (door ajar switch ) is an input to the SMJ - smart junction box or body control module take your pick .
Principles of Operation
When the SJB detects a request for lighting, it turns on the interior lamps by supplying power to the lamps. The request for lighting can be an open door signal from a door ajar switch, an interior lighting on command from the instrument panel dimmer switch or an unlock command from a remote keyless entry (RKE) transmitter.
The door ajar switches are hard-wired directly to the SJB. The 2 door ajar switches are normally closed when the doors are closed. The decklid ajar switch is normally closed when the decklid is closed. All door ajar switches receive voltage from the SJB and each has its own ground circuit.
The instrument panel dimmer switch receives a ground signal from the SJB. The instrument panel dimmer switch provides variable resistance for backlighting the instrument cluster and a toggle ON/OFF function for the interior lights.
The RKE receiver is contained inside the SJB. When the SJB receives an unlock request from an RKE transmitter, it unlocks the doors and turns on the interior lamps. There could be DTC'S diagnostic trouble codes stored in the SJB ! You can not access these codes with a OBD2 code reader , need a factory scan tool .
B1319 Driver Door Ajar Circuit Failure Go To Pinpoint Test D . B1327 Passenger Door Ajar Circuit Failure Go To Pinpoint Test D . B2021 Dome Lamp Input Return Circuit Failure Go To Pinpoint Test A . B2550 Dome Lamp Output Circuit Short to Ground Go To Pinpoint Test A . B2554 Dome Lamp Output Circuit Failure Go To Pinpoint Test D . Do you know B-codes -body control .
Your best bet is to take to a ASE certified repair facility or a Ford dealer .

alarm will obviously sound because the anti theft device thinks door is open...maybe it doesn't think ...it mis detects
check the door light switch and how it is affected by closing opening of door. look at what happens at the contact point.
It may be something mechanical, or something electronic/electrical
empirical testing should reveal the answer

I HAD THE SAME PROBLEM WITH MY REAR DOOR TAHOE 2001 ., I TOOK IT TO THE MACHANIC AND IT WAS SO SIMPLE A FUSER UNDER HOOK . $8.00 FUSER ., IF I WOULD IT KNOW . I WOULD IT DONE IT MYSELF.-- REPLACE FUSER WHERE IT SAID --HORN- ITS UNDER THE FRONT HOOK... I END IT UP PAYING $120.00 FOR THEM TWO HOURS WORK...THE LIGHTS AND THE ALARM WAS NON-STOPPING MAKING NOISE..... RIGHT..????

you have a faulty auto alarm system have to have it tested

Replace the drivers door switch, it's shorting out. It's on the B-pillar below your door latch, covered in rubber that you can pull off to get access to it. You can take it out, just tie a string to the electrical connector and tape it to the door so you don't loose it. The switches are fairly cheap at the dealership.

spray the door latch with WD - 40 on both doors then open and close multiple times. Sometimes they get stuck ond this help if they free up once a month should keep it away

there is a switch in each door that senses the door is open, it is called the door ajar/courtesy light switch (imagine that), they stick and have this problem, replace it.

The door switch is stuck on or the wire is shorted to ground.

Hey,try this. Get some WD40 or equivalent and spray it inside the door latch.Then open and close the door a few times. Do this on every door. Note which door the you sprayed when the door ajar light turns off because that will be the door latch you will have to replace. What happens is that the door ajar switch sticks.