Not exactly. The current flowing through the #1 plug is compared to the total current flowing through 2-5. If the ratio isn't 1:4, then the indicator light is turned off during the preglow cycle, but will come on later.

The result is very wonky, because the way that current is measured is with two coils on either side of a magnetic switch. One coil has 4 times the number of windings on the other, and is counterwound. These coils supply power to the plugs. When ratio of the currents is exactly 1:4, the magnetic fields created by current flowing through the coils are equal and opposite, and the magnetic switch isn't activated. So odd situations can occur when more than one plug is bad, or when the resistances aren't all in spec. My policy is to replace all the plugs whenever the lights go nuts.