I've recently purchased a 1987 pickup and am still new to working on cars in general, please excuse the poor explanation. After driving around for about 20 minutes on the freeway going about 60 mph with overdrive on the transmission would shift back and forth from what I would assume is 4th to 3rd. this would happen every 5 or so seconds. While this was happening I heard an arcing noise coming from the area around the brake pedal. i just did some troubleshooting following the guide attached and found that the wires for ports 1 (blue) and 3 (black & red) did not give any voltage with the overdrive button on. i later found that there is a 3 prong connector that is just laying in the engine bay near the fuse box. am i on the right track? please help, thanks!

 

do you have the users manual ?

 

No I don't but it hasn't done it in a while. hopefully never again.