Up till OBDII all you stood to lose was the performance of your feedback control system. This usually only tranlated to poor mileage and premature catalyst failure.
With OBDII the cars control unit will rat on you if you don't hit the design characteristic precisely. It will probably only cause the engine light to light after the thing gets older, but you never know. Achieving operating temp is part of the design and location of the sensor. You are playing roulete just hooking up the same number of wires.
Bosch Master, ASE Master, L1
33 years MB technician