Looking for a connection to ground
On most HD equipment the running lites can be the marker lites or the lower body lites. The first task will to locate the fuse or breaker that protects this circuit. If the circuit uses fuses, make up a short pair of wires using a 20 amp circuit breaker between 2 aligator clamps. Remove the fuse and use the breaker in place of the fuse. Using the breaker will allow the circuit to be tested many times without replacing the fuses. Having a helper will valuable. After the breaker is in place, go outside the vehicle and look at the lites. Have a helper turn on the running lites and observe the lites that work. If the breaker opens, allow time for the breaker to reset and check the rear lites. Same drill and observe the lites, looking for the lite that does not illuminate. If this test does not produce any good results, start disassembing each lite. After checking te lites, do not reassemble but go to the next lite. If no obvious arcs, wire burns or wire welds to ground, keep trying the running lite switch, and watch the lites. With all the bulbs removed, try the running lite switch again. If the breaker does not open, slowly install the bulbs untill a fault/ground are found. If all the bulbs are replaced and the lites are on, go to each lite and bump with rubber mallet, around lamp to make sure the problem is repaired. WD40 is a good electrical spray on electrical contacts. Each lamp base should have a little dab of dielectric paste to ward off any moisture. Moisture creates rust and corrosion which is not good for electrics........... Frank from Idaho
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