From what you are describing I am assuming a seat is a switch (never read that term before). Not knowing your circuit I cannot really suggest either a pull up or pull down. When the "seats" are open that tells me you have an open line. That would explain what you are seeing. My way of doing it would be to put a pull up resistor on the switch and use ground on the other side so when the switch is closed the line to the Arduino is grounded. That will invert your logic but that is an easy fix in software. Maybe ~500 Ohm would work OK.