Door ajar light is not monitored so it can be removed, but straying some WD40 in the door usually fixes that sensor
Google: Ranger door ajar
'03 Ranger 4.0l will be the 4.0l SOHC engine, found in Rangers from 2001 to 2012
2000 and earlier Ranger used the 4.0l OHV, which is completely different engine.
Manual trans for the 4.0l SOHC was the M5OD-R1HD
But you could use any 4.0l, OHV or SOHC, M5OD-R1 from a 4WD in your '03, the "HD" means it has an extra bolt hole in bell housing.
All the M5OD-R1 transmissions have integrated bell housings, this means an M5OD-R1 from a 3.0l engine will not fit 4.0l, and visa versa.
2WD and 4WD transmissions have different tail shafts, not a Ford thing, any brand is like that, so you also would need a 4WD trans
M5OD-R1 is often called M5R1
For larger trucks Ford used the M5OD-R2, M5R2, this will not fit a 4.0l as that engine size was never used in larger truck, i.e. F-150 and up
Transfer case is a Borg Warner 1354, or BW1354, used on Rangers since 1990.
2003 was the last year Level II came with manual transfer case, there were problems with them, just FYI.
2004 and up Level IIs all had electric shift
Electric and manual are not interchangeable, shift shaft is at a different location.
But there were manual shift BW1354 used in Rangers until 2003.
And you could use a BW1350 in a pinch, manual of course.
Issue with different year transfer cases is the drive line connections, there were 2 kinds.
2000-2004 would be rear circular flange, front cup yoke
Level II will also have Torsen rear differential, these were better than Ford Limited slip(trac lok), and tend to last a long time if maintained, like most things, lol.