If a brake switch is malfunctioning could it keep a truck from startin

Hello Donna , i think you are thinking correctly, some cars , especially with bigger engines , won’t start unless the brakes are applied, and the gears are in P or N . but what varies is whether it’s an automatic car or manual , whether for manual - some require clutch pedal to be pressed in to start . also the water in the intake might have messed up slightly, i don’t know if it’s not starting at all, or spinning the starter motor and not starting the engine? . whats important is that your brake pedal switch is a NC ( normally closed) circuit that is pressed all the time when brake pedal is up , making it open circuit , closes the circuit when pedal is pressed ( brake light lit up) . if you did played with the wiring, can you check if the switch has only 2 wires connected or more ?