Hi,
The ABS warning light has come on and the speedo has stopped working ( plus management light)
I have read the diagnostic codes and get P0500 and P0121.

From what I have googled, I am guessing it is likely to be a speed sensor but would this be on one of the wheels, or on the gearbox? Would I have both?
Also I have looked up the P0121 code and it refers to "Throttle Position Sensor Switch". I have absolutely no idea what this might be. Can anyone shed any light?

Many thanks, Graham