I have a fiesta brake master cylinder with 4 outlets, 2 are a different size to the other 2, Is it better to run 4 separate brake line to each wheel or only run 3 and block one of? also does it mater which goes to which wheel

If its a kosher Fiesta mcyl, there should be a 50:50 split between primary and secondary chambers. Fiesta brakes were connected in X-split (i.e. L/H front to R/H rear, R/H front to L/H rear).

Primary = nearest to pedal,

Secondary = furthest from pedal.

Check out the displacement vols for your brakes cyls.

Hi, replaced my sierra m/c with one of these (bought from lurch88 off here) which had the larger outlet at the pedal end blanked off with a bleed nipple. I used the other 3 outlets and the car has just passed its MOT without any issues.
Cheers
Ray

Could use the fourth port for a brake light switch.I have fitted one of these gives more padal movament ans less effort because of the smaller bore size.

I've done as RSmith too with the bleed nipple. Far better response than a Sierra MC.