hi fellow lexus owner its common for the wipers to over run and miss the park switch because the small wiper blades dont put enough load on the motor and momentum keeps it rolling past the park switch. or it may be wired wrong .
it is probly the bigest problem i see with cobras. and it depends on what switch you are using don at snake bite has the proper lucas switches and supplies a wiring diagram if you want.
his number is 07 5529 0877. he has just about anything you could want to finish a cobra . great quality gear.
regards Scott.