Horn doesn’t work
If the horn in your GMC truck doesn’t work, here are a few tests and some results shops are seeing. First, supply power directly to the horn, bypassing the horn switch, horn fuse, clock spring, and horn relay. If the horn honks, that confirms you’ve got an electrical problem somewhere else.
Next supply power ground the tan wire for the horn relay behind the clock spring. That ground wire goes to the control coil in the horn relay. If the horn still doesn’t work, pull the horn fuse and check for corrosion in the fuse box. Tech are reporting corrosion in the main fuse box causing all kinds of electrical problems. In most case, the corrosion is NOT repairable and you must replace the entire fuse box.
© 2012 Rick Muscoplat