I used electrical cleaner on mine and it did the trick. I am not sure how great wd40 is on electrical connections. I had the opposite issue though my light would not go off when the door was closed. maybe the problem is somewhere else besides the latch. I have seen a thread for repairing that switch I just cant remember where Google it it
2004 Ext Cab, 4WD, 4.0, Auto, 146k. (4.0 engine is out of a 2009 Ranger w/96k) ( as of 3/10/2016)
2004 Ranger, Ext Cab, 2WD, 3.0, 5 speed , 4WABS, crank windows, no cruise, Edge 116k.(6/5,2014) (SOLD).
1999 Ford Ranger, Reg Cab, 2.5, 5 speed, 2WD, no AC, 150k (SOLD).