Use an ohm meter, not a voltmeter. And to add to the story, besides just being a long piece of wire wound up, there is likely to be a resistor across it if it's a GM relay, and a diode if it's a normal relay. The coil will produce a voltage spike when it is turned off, just like an ignition coil. Resistors dampen those spikes but since they have no polarity, the coil can be wired in either way. That's why GM relays can be installed turned around and still work. Diodes short out those spikes very effectively but will not be turned on by the low voltage supplied by the ohm meter, so you can read the coil's resistance. I never looked at the resistor in a GM relay to see what the value is, but it will affect the reading when measuring the coil. Relays with diodes can only have the coil wired in with the proper polarity, not because of the coil; because the diode needs to be in the circuit backwards so it will not conduct except for those spikes.
Regardless, you are looking for an open circuit, (defective), or some value of resistance. That value isn't really that important since the coils don't short very often. The two ends of the wire are at opposite sides of the plastic form so it would have to overheat over a long period of time and burn the varnish insulation off the wire before it would melt into a puddle, so to speak.
Tuesday, December 7th, 2010 AT 8:07 AM