First to clear up terminology.

A "short" ( circuit ) is where a power source output terminals are bridged with a low resistance conductor. If you took one jumper wire and attached one end to the + and the other end to the - of your battery, that would cause a "short" and a shower of sparks.

A "open" ( circuit ) is when a wire is not connected and the system just sits there.

One quick test is to attach an _incandescent_ lamp to the glow plug terminal and see if it lights up every time you glow. I don't have a diagram or diagnostic for your system to go any farther.