Taxiing for takeoff in an MD80 one night noticed the strobes were flashing and the idle power was stuck in approach idle, not ground idle. I did not realize that I had also lost my takeoff warning system at that time. Apparently maintenance had over inflated the nose oleo strut making the aircraft think it was in air mode. I used an agressive brake application to compress the oleo strut and everything went back to normal. In this case the R2-5 relay probably failed, not the oleo strut switches or they would have noticed the approach idle power as I did. It was daytime so probably wouldn't have known the strobes were on if both oleo switches failed in air mode. With the intensity and damage from the crash it probably would not be possible to determine for sure if R2-5 failed or if something upstream of the relay failed.