Unplug the relay, being careful no to break the lock tabs.
Identify the two control circuit terminals and the two power circuit terminals. Most relays have a diagram printed on the case itself to identify these terminals. If not, look at the mounting base of the relay. The two thin-gauge wires that connect to the relay feed the control circuit terminals; the other two thick-gauge wires connect to the power terminals.
Test for continuity between the two power terminals on the relay. Using an ohmmeter, set it at the lowest resistance range and touch the meter leads to each of the relay power terminals. You should read infinite resistance; otherwise, the contact points are shorted. If this is the case, replace the relay.
Connect the end of a fused jumper wire to the positive terminal of the car battery (see the Tips section bellow) and the other end to one of the control circuit terminals on the relay. Hook the end of a regular jumper wire to the other control terminal and touch the other end of the jumper wire to a good ground on your vehicle (this could be the engine block itself). As you touch ground with the wire, the relay should make a clicking sound. If not, swap the jumper wire connections. If you still cannot hear the click sound, the relay is shorted. Replace the relay.
Leave the jumper wires connected to the relay control terminals and test the power terminals for continuity as you did in step 4. This time you should read zero or a resistance value in the hundredths or thousandths. If you read infinite resistance, replace the relay.
Friday, April 30th, 2010 AT 2:18 PM