Chevrolet Repair Questions? Ask a Chevy Mechanic for Answers ASAP
hello I will help you with your question,
Can you check at the rear junction block up by the spare and see if you have 12 volts on the light blue wires in the harness coming from the front of the truck with the brake pedal down (third light on)? If you have 12 volts replace that rear junction block and clean any corrosion from the connectors that you find.
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Do you see any corrosion on the connectors? Can you check at the bulb sockets to be sure the 12 volts get up to them?
Then there must be a break between the box and the lamp connector or the ground that comes back through the box is broken. If you measured both pins at the lamps for light blue and checked it to ground then the break is in the light blue between the box and the lamp connectors but for both to not show 12 volts I would be looking at the connector into the box closely.