1987 Ram 50 O/D not working

I have a 1988 mm with a 1987 d50 2.0 auto transmission. I know there's been several posts before but, for some reason my truck won't go into overdrive I didn't know if anybody had any insite on what direction I might go in order to fix the problem. It shifts fine from 1st thru 3rd and weather the button is on or off the overdrive will not work. I've heard of grounding out one of the sensor wires but I'm kind of skeptical of doing so because I don't want to burn anything up. I've also heard that there is a relay on the kick panel drivers side that can go bad. I'm just looking for some options then I can check out without having to take the truck apart in order to find the problem any help is appreciated!

There is a sensor on the intake manifold near the carb that tells the tranny that the motor is warm enough to go into o/d. That sensor grounds the wire to get the o/d to work - that is why the quick fix is to ground it to see if the o/d works. The only thing that the sensor does is delay o/d, grounding the wire lets the o/d work anytime -it will not hurt the tranny - it was an emissions thing.

I appreciate it Pennyman1. I'll give it a try. I'm just skeptical with my run of luck!