From memory, i believe the following is correct... (though i easily could be wrong!)
the "start" tap is the center tap. Everything but 120 volts is reference to this lug. Meaning when measuring transformer AC outputs, the center tap is where one of the DMM leads attaches.
The "high" and "normal" are the coil voltages. 28 volt AC and 30 volt AC respectively.
The "1" and "2" taps are light voltages. Gottlieb used 6.3 vac for everything except for the coin door, in which the voltage "2" is about 5 volts. Why did they do that? Because the lower voltage will keep the coin door lights alive without burn out for a really long long time (though obviously not as bright.) They did this because it's a PIA to change the coin door lights, and operators generally never did it. Without coin door lights, the coin slots look "dead" and in theory, the game does not earn as much.
Lugs "3" and "4" are AC voltage in, meaning 120 volts. If you put your DMM on these two lugs, you should get line voltage (that is, don't use center tap as a reference.)
Note the above transformer is not designed to run at anything other than 120 volts. Mean Gottlieb used an entirely different transformer for 220 volt applications (with different lug designations.)
To verify my theory, just use your DMM set to AC voltage to check. You'll know quick enough if i'm right or wrong...