Trailer lights

Check fuse 67, a 20-amp, in the under-hood fuse box by the battery.

When customers are paying for our time, we do not have time to waste trying to figure out which one or two fuses to test. It is much faster to just grab a test light, then poke it on the two test points on top of most spade-type fuses. For this circuit, it is always live, so the ignition switch does not have to be turned on. The light switch also does not have to be on. If you find 12 volts on both test points, that fuse is okay. If you find 0 volts on both points, that circuit is currently turned off. You are looking for a fuse that has 12 volts on one test point, and 0 volts on the other.

An even faster test is to remove the "parking lamp trailer tow relay", then test for 12 volts on the terminals in the socket. Be careful to not stick the probe in so hard as to stretch the terminals. Doing so will cause intermittent problems in the future. You don't even have to know which terminal is which. One must have 12 volts all the time. If none do, check that fuse 67. A second terminal should have 12 volts when the head light switch is turned to the tail light position. If that is missing, check fuse 40, a 10-amp, in the Body Control Computer by the right kick panel. In this case that one should be okay. If it was blown, the truck's tail lights also wouldn't work.