How to interface DS1801 digital resistor with Arduino DUE SPI interface? What clock rate so use?
There is no way in hell you're going to get a 10MHz signal down that line. Shorten it to 3 inches total maximum and reduce the clock rate to 2MHz or lower. It is possible to get a 10MHz signal through, but you'd need to switch to twisted pair wiring and proper termination to even begin to have a chance to get it to work.