Volvo: Electrical problems, spedometer, loose ground

Question
1991 240 wagon - air - Automatic, had it since new and it has 403,000km.  The gages, spedometer and idiot lights failed to-day.  The overdrive arrow on the instrument cluster was on when I started the car.  The car ran fine.  When I pressed the overdrive button to activate the overdrive the Battery light illuminated and the spedometer started to pulse, still no Fuel or Temp.  I drove home and checked the fuses- all fine.  I drove the car into town and pressed the overdrive button and suddenly the whole thing started to work fine.  Is there a loose ground?  if so where do I look?  The overdrive relay looks fine (I took it apart)The engine ground is attached properly.  Any suggestions would be greatly appreciated.
thank you Robbie  

Answer
This definetly sounds like an electrical short.  My guess is that it is occuring either from the shifter button to the relay, the relay to the back of the instrument cluster light, or from the relay down to the solenoid.  The wires that run by the transmission on the underside of the car can be exposed to heat and crack their insulation, causing shorts.  I would inspect the wires for breaks like this.  Good luck!