The metering blocks on Mustangs (similar on most cars of that era with dual systems) have a central pin that blocks the failed side of a braking system & activates the switch. On the early Mustangs, if the pin went to the rear, it could be difficult to get it out as there is no opening at the rear to push it forward.
The method I use is to fit a grease zerk (nipple) to a brake line fitting & then screw it into the (removed) metering block, at the blocked end. Note; I have also removed the front brake fitting that gives access to the internals of the block.
With the opposite hole (that would have been the outlet) blocked, attach a grease gun & pump it out. Hydraulics in action .......
Now all that remains is cleaning the metering block of all the grease (takes longer than removing the pin .......
), testing you have assembled correctly (I use a voltage meter across the switch to see if I have centered the pin) & fitting back on the car & bleeding the brakes using gravity or vacuum (never pumping the pedal ).
