If a coil diode is installed backwards you'll know it quickly, because it will short coil power directly to ground and usually taking out a coil power fuse.

Diodes across a coil are always reversed biased. (cathode, or striped indicator towards coil power). In almost any game the coil power is a fatter wire daisy chained to multiple coils. If you can't Identify it visually, use a schematic. If you don't have a schematic, you can unsolder the coil wires and use a voltmeter to identify the power supply side of a coil.