Originally Posted by
Andy
I would assume you'd hook a sensor to it (either a voltmeter or just a simple light that lights up when it gets signal), if the relay is getting a signal from whatever is supposed to turn it on but the function isn't turning on, the relay's probably bad. You don't hear of many relays failing but I'm sure it happens.
Never use a test light on a vehicles electical system!!! they are not safe to use in an automotive environment. it may damage your vehicles computer. always use a multimeter/voltmeter when testing.