While driving my '91 940 turbo, the 4th gear disengage comes on randomly and won't let me turn it off. Sometimes it turns off without any problems but recently it comes on when I start the car and stays on the whole time, it's becoming a real problem since I'll be driving around 50 mph and pushing over 5000 rpms. Do I need a new tranny or is there a different problem? PLEASE HELP I'm driving across the country later this month to start a new job and would like to be able to use my 4th gear on the way.

 

This sounds like the overdrive relay to me. I would find it and try to unplug and replug it in. If that doesn't work I know you can jumper it out so that OD works. I did this when my relay went and drove it for a while until my new relay came. I don't remember the jumper off hand but it was easy to do.

 

Agree - most likely it is the OD relay. Best would be to get a replacement (new). What usually goes wrong on them is the solder joints get cracked. You can repair them if you have a soldering iron. Just pull the relay out and pop it open. Resolder all of the points on the little circuit board.