Oil pressure warning light is ON!

[FFGREG32 at aol.com]

Hi, just retrieved my car from the local independent foreign car mechanic in 
town. I had the thermostat replaced. As I drove away, my autocheck system 
beeped and displayed the oil pressure low signal. I drove to a place where I could 
check the level, and it is ok. The gauge in the cluster shows normal oil 
pressure, and there is no clatter at the top end of the motor, nor any other 
abnormal symptom. Could the "tech" who installed the thermostat have unplugged a 
sender or something? Any ideas? Thanks in advance, Greg
1989 Audi 200TQ (Former Andretti car)