Volvo: Overdrive, switch button, shift lever

Question
1993 240 Overdrive does not engage -  dash indicator light on all the time - have checked relay and switch by exchange with working units in another car - relay clicks when switch button is pushed.  I suspect wiring damage somewhere below the shift lever.  How does this come apart and how to check out wiring ?  We are 100 miles from a knowlegable shop and the car is about 450 miles from home So I will try to repair myself if possible.

Any/ALL help GREATLY APPRRECIATED.
Thanks,  
Marvin

Answer
theres a white wire down on the transmission , left side on mine anyway , i have an 87, the wires might be dirty or corroded or shorted out? not really sure about under shifter. as long as you get the 2 plastic trim pieces off the shifter then you can take other stuff off.