How can I fix my overdrive? It doesn't work weather the OD light is on our off

Not sure where any of that is located. I'm pretty good with engines, not so much with transmissions. I bought the truck from a guy who used it just as a farm truck. So he probably didn't have much use for an overdrive. I did get under it and noticed that a wiring harness with three wires had a blue wire that was severed somehow. I spliced it back together, but apparently there's something more going on. I've heard that it could be a solenoid problem and that it's inside the fluid pan. I've also been told it could just be a sensor. I'm just looking around looking to get some ideas on what to do about it. Any advice I can get will help, I'm sure. As I said, I'm just not a transmission guy. Thanks for your answer, and thanks in advance for any further advice. It will be greatly appreciated. I'm hoping I can fix the problem because I do like the truck.

You're in the right ballpark, but unfortunately, testing will be needed to find out what's going on. If there was an electronic failure, i'd expect possibly a warning light of some kind to be indicated. Hard to say due to the model year of the vehicle. Yes, probably will need to test solenoids and check for debris in the transmission pan from a possible mechanical failure.

Thank you so much for your advice. I'm trying to go about it as cheaply as is possible as I'm on a very limited income. I have a friend who is a professional mechanic, I believe he has several of those handheld diagnostic code readers, maybe he can pinpoint the problem and maybe assist me in repairing it. Again, thank you for your replies to my question,you have been very helpful. I will be using this app allot more often