The inputs are from brake, left and right indicators etc. so the inputs can be very short pulses if someone touches the brake for a fraction of a second hence why I was using the on change interrupts to catch all the inputs.
The inputs are all held low by resistors (not high as i put before).

I'll try the answer that bruce & Co have offered and see if i can find the answer to my problems.

Thanks for the support guys it's kept me sane


Rob