Here's what I wrote re. overdrive wire repair earlier.

Overdrive - Auto Trans

In my experience, the most common overdrive problem is a broken wire leading to the solenoid.

Wire goes (in my '86 and '89 Auto Trans 240's) out the shift lever box at it's front end, down past the driveshaft on the passenger side. Goes forward along the pass. side of transmission, crosses somewhere, then goes along driver's side of trans. fluid pan to finally meet the solenoid. I had 2 of these wires break where they go down past the drive shaft. Fixing is a pain unless your hands are the size of a five-year-old's.

IF you have a broken wire - -
My solution - Push new wire forward out the front of shift lever box using needle-nose pliers. Push out about 6" or so. Then get under the car, find your new wire, pull it down, and join to what's left of the original wire. Use good connectors, and shield with vacuum tubing as needed to protect it.

Of course, splice new wire onto the old in shift lever box. It's white on the cars I've seen. Wire comes down from glove box area (from relay) into the shift lever box. It's the only one there that has no other function in the shifter box. The others are for the indicator light, and for gearshift position detectors (auto trans) for Reverse and Park/Neutral, and a ground wire.

Pushing it out using pliers is a pain, but better than removing the rubber grommet on the shifter box, which makes pushing wire thru a real easy task. Problem is, you'll never get the grommet back in, and so will get engine noise and wind up thru the shifter box. That's how I did it the 1st time. I used some putty to substitute for the gasket, which worked OK.