This infra red phototransistor replaces Williams part 5163-14114-00. It is used on opto sensors and ball trough receiver boards. Opto problems usually stem from the emitter, but these also occasionally fail.
These parts have the correct shape for Williams games, and are chosen for high sensitivity.
For installation, there is a little tab on the package that must align with the outline on the circuit board and the letter "E". The orange wire goes to the E, and the grey wire to the C.