Also a good idea to replace the diode when taking a coil from an old machine to use in another machine. EMs don't use diodes on coils but are a requirement for most SS pinballs (some cuircuits have diodes on the board) best to check the manual.
For EMs a SS coil e.g. a common 23-800 can be converted for use in the EM simply by cutting off the diode.
But remember if an SS coil requires a diode then you will cook components on circuit boards by not having a working diode in place! And often the damage will go further back than just the driver transistor!