My wife's 1993 240 has had some trouble with the overdrive light coming on. I took it out and resoldered the connections on the circuit board that looked possibly cracked and for a few weeks it was fine. It has just resumed this behavior again today.
Whenever the OD light is on, there is a whining noise coming from the dashboard that sounds like it is in the vicinity of the relay. Repairable (did I miss a cracked bit of solder?) or is it just time to chuck it and buy a new one?