[1971gmcshortbed]

Hi Monte Carlo, the tpm system on that Monte Carlo doesn't use sensors, this is how that one works:

The Tire Pressure Monitor (TPM) system alerts the driver when a large change in the pressure of one tire exists while the vehicle is being driven. The TPM system uses the Electronic Brake Control Module (EBCM), ABS wheel speed sensor inputs, class 2 serial data circuit, and the Instrument Panel Cluster (IPC) message center to perform the system functions. The EBCM contains the software to calculate relative tire pressure differences. The software requires approximately 30 minutes of straight line driving in each of the three different speed ranges to complete the calibration process in order to have full capability of detecting a tire pressure condition.

(info courtesy of General Motors), I can see how that system will turn on the light with a rotate if the system is not re-set. I measures the circumference of the tires with the speed sensors at each wheel. A low tire obviously is shorter and spins faster than an aired up tire. Also a new tire is taller than a used tire. That system is reset with the light switch, radio, or tech II scanner depending on how it is setup. Thanks for the input, take care bud,