No you do not test the light, you test the light "socket" There are two places the bulb make contact. Electricity goes from one contact into the bulb and then from the bulb into the other contact. So with the bulb removed you should be able to see it. If it is not clear, because sometimes it is hard to look inside the small space, then look at the bulb and then the "socket" You can use either a multimeter or just a test light. The test light looks like an icepick with a wire hanging off. There is a light inside the handle. Either put the ground from the multimeter or the wire hanging off the test light on anything metal that is connected to the trucks body or frame (that is the gound or where the electricity goes). Then take the positive connection from the multimeter or the sharp end of the test light and touch the two connections inside the socket one at a time. When you touch the ground connection it will not do anything no matter what you use. When you touch the positive connection the multimeter when set as a voltage meter will give you the voltage, the test light just lights up. Test lights are cheaper and I do not have to worry about the settings on the multimeter. The light is either on or not on. You can see how either work by testing on a good battery. Touch the negative on the battery (it is the ground) and then the positive on the same battery. If you are using a multimeter it should show about 12v if not check the settings on the multimeter. If you do this with a test light you will see the little light come on. Now use the front battery put the ground from the multimeter or test light on a piece of metal attached to the truck almost anything under the hood and then the posive to each side of the battery. So when testing the connections you are testing the same thing, you are testing to see which side of the battery the connection is connected to. That is how you know what is positive and what is negative.
