Yes joining the connections with a wire is known as a "short-out". Shorts are very destructive as you have learned.
You should also know there are voltages at the edge connector like 12volt that will destroy chips.
Dont plug ZX81 interfaces into spectrums or vice-versa i bought a interface II from trademe guy told me he had been trying spectrum interface in zx81 and showed it working on trademe, he delivered it to my place,went inside, had spectrum setup, plugged it in and DEAD !The guy had shagged it in his zx81 but i guess he really needed the money becuase he keep it quite, i was afraid of getting negative feedback so i left it alone. He then sold some other dead items admitting on one auction he had shagged it plugging it into a zx81,
Check with uncle google first next time and find out what happens before you experiment.