Need HElP !!!!

I posted earlier about my 740 GLE not going into overdrive, but still cant figure out the problem. It had this problem once in a while when I got it about 2 years ago. The overdrive lockout light would light up on the dash and then it refused to go into overdrive when I pressed the button. After enough fooling with the button, or just by luck the light would go out and it would shift into overdrive.

Now the light stays lit most of the time and I dont have overdrive at all. I had the transmission fluid flushed/exchanged at a local shop about 6 months ago, and have replaced the overdrive relay behind the fuses with 2 differnt ones from a local yard, and I dont assume I could have a total of 3 bad relays. Sometimes the light will go off, but still no overdrive. I have also pulled the overdrive switch out of the shifter handle to try and by pass it thinking the switch was bad, but with the circut open or closed via a wire loop, the light stays lit.

Any other ideas on what it could be....any place to look for broken wires? Does the transmission get its shift points from the speedometer? As mine has also quit working, but it will have to be a little warmer here before I get a chance to crawl under and check the wires that run to the rear diff. Can the overdrive relay be bypassed?

Any ideas would be greatly appreciated....thanks