i had this problem with my 1997. it wouldnt go into overdrive and the o/d light wasnt on. i took apart the shifter to find that none of the wires (red, black, or yellow) were connected to the switch. just connect he red to the black and see if you have o/d. thats how i fixed mine.

 

I had the same problem with my 2000 venge. No OD light on the dash regardless of switch position and no shifting into overdrive. I was looking for a fuse that might be blown and the only one that was bad was the one labeled "back up light". I replaced it simply because it was bad not expecting it to have any effect on my problem, but lo and behold....the overdrive worked again!