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This is caused by at least one bad headlight ground. The current backfeeds through the bulbs' high-beam filaments (which don't get hot enough to glow) and then to the dash indicator. The grounds are the same as shown in this diagram:
Was the truck ever wrecked? Is there battery acid damage on the core support? Any aftermarket wiring mods, like a big bumper, lights, winch...? Has it spent much time near the coast exposed to salt? More information in your profile & signature would be helpful.
Was the truck ever wrecked? Is there battery acid damage on the core support? Any aftermarket wiring mods, like a big bumper, lights, winch...? Has it spent much time near the coast exposed to salt? More information in your profile & signature would be helpful.
