Direct from the manual:
TPS 1 decreases in voltage.There are 2 individual TP sensors within the throttle body assembly.
The TP sensors are used to determine the throttle plate angle. The TP sensors provide the engine control module (ECM) with a signal voltage proportional to throttle plate movement. The TP sensor 1 signal voltage at closed throttle is near the 5-volt reference and decreases as the throttle plate is opened. The TP sensor 2 signal voltage at closed throttle is near the low reference and increases as the throttle plate is opened.
TPS 2 increases in voltage.
Does it matter which I tap into so long as I know the voltage range? Is there a preference?
Also, there is an Accelerator Pedal Position sensor. Would that also work as a TPS reference for RaceCapture? It'd make wiring easier. It has 2 sensors, but they both increase in voltage.