Volvo Repair: 88 740GLE Auto only runs with three gears, overdrive switch, volvo 740gle

Question
Dear sir,

I am having problem with my 88' Volvo 740GLE. First of all I have to tell you that I am not a machanic and most of the knowledge and the terminology I use to fix this car are mostly from the volvo repair manual. Short history about the car, my dad's 740 had broken down for almost two years without being started at all until I finally was able to crank it up (really lucky- I just cleaned the feul pump relay). I tried fixing it to pass the inspection. The automatic shift was loose. It wouldn't stop completely at "R," and the back up light would only light up when I shift pass it- not when completely shifted to R. I fixed it by replacing it with a shift lever of a 760 turbo from the junk yard, wihch still had two rubber rings attached to the gear's linkage. I also put a new rubber ring to the actuator rod linkage. The reaction rod is still without the rubber ring.

After I changed it and connected all the wires. Now I am able to get the back up light to work and  the gear completely stoped at R position. But now it only runs with three gears and the overdrive does not work.

I checked the overdrive wire the connection and the overdrive switch that is attached to the lever. It looked fine- no wear and tear. I also notice that the switch makes soft noise everytime I pushed it, which shows that the switch is working. The shift lever from the 760 seems to have an extra wire from the four sodering point at the left of the lever and It took the space of the pink wire so I cut it out and put the pink wire into the connector instead.

Thank you very much in advance for your response and input.  

Answer
most common is a bad relay for the overdrive. below is how to change the realy


the overdrive  pump relay is located on the fuse panel behind the ashtray.remove the ashtray and then remove trim around lighter socket then you will see 2 screws remove the screws and the storage area will come out the relay is white and about 1x1x3  inch.it will be towards the passengers side of the panel.