What is the ruling on the transfer of impurity in the event of squeezing the male organ and liquids splattering onto the hand, and then touching the steering wheel and door handles, etc.? And what is the amount of moisture that transfers impurity?

It is clear that the questioner is afflicted with waswasah (obsessive whispering), and he must be cautious of it and not give in to it. If he is not certain that what touched his hand was madhiy (pre-seminal fluid), then there is nothing upon him, and it could be sweat or something similar. If he is certain that it was madhiy, then he should not rule that the impurity has transferred to what it touched unless he is certain that one of the two objects was wet. Some scholars hold that impurity does not transfer in such a case, and there is no harm in adopting this view to repel waswasah. Assuming the impurity did transfer, there is no need to purify anything to which the transfer of impurity is not certain, as the default is that it has not transferred.