Are the GP's in the 84 wired in series? If so, then touching each glowplug probably fried them, since you were applying 12V to something that was only designed to handle about 2.5 volts.
And if they're wired in parallel on the 84, then they would have been fine, and you can ignore me
I agree that "jumping" the GP's like that is dangerous. Why? If your positive cable accidentally comes in contact with anything metal on the way down to the GP, you'll get a direct short to ground. Kinda the same rule as always connecting the positive terminal first on the battery. If you do the negative first, then everything metal is negative. If you hit something with your wrench while tightening the positive terminal, you'll have a wrench welded to some part of your car. There are probably other reasons too.