Wiring and horn problem on 66 c10

[Jmh2fb]

Hey all,

New member and heck of a mess on my hands. Got an old 66 c10. Wiring harness was partially fried (purple wire), blinkers didn't work and one brake light (driver's side) wouldn't light and horn unplugged. Purchased a new wiring harness and turn signal indicator, replaced blinker fuse and bulb. Good news is that I have blinkers, but still no brake light on driver side and when I plugged horn it blew constantly. Took turn signal switch back off with steering wheel of course and can only get horn to quit if I unplug horn or if I move steering column by pulling to side. (As a side when you hit brake lights with turn signal on turning right the left tail lights)

Any ideas? Multiple issues? Related? Help!

[ray_mcavoy]

Welcome!

The horn issue sounds like a short to ground somewhere in the black wire that connects the horn button to the horn relay. The horn button normally grounds that wire to complete the circuit to ground and energize the horn relay. So if that wire is shorted to ground anywhere along the way it'll keep the horn blowing all the time.

Since pulling the steering column to the side makes it stop, I would recommend that you start looking in that area. Check to see if that black wire accidentally got pinched somewhere (such as between the column & dash).


The tail lights, brake lights, and turn signals are probably an unrelated issue. The first thing to check there would be the grounds at the light sockets.

Tail light grounds are a very common problem on these trucks because the stock configuration relied upon the metal tail light housings to provide the ground. That in turn requires the housings to make good electrical contact with the truck bed, the bed to make good electrical contact with the frame, and finally the frame to have a good ground connection to the negative battery terminal. Paint build-up, rust, and corrosion at the contact points between those various parts often leads to poor grounds at the tail lights. Many folks have chosen to run dedicated ground wires directly from the light housings to the frame to ensure good grounds.

[Jmh2fb]

Thanks Ray. You were right. The steering shaft was up against the housing. Apparently there is a sleeve that goes around this although it didn't exist. I improvised with a garden hose. I cut a 4 inch long section and slid it over the shaft between the housing. Problem solved!

As for the lights a much trickier endeavor. I tried grounding wires but still no brake light on one side. Then I noticed that it lit when opposite blinker was on. With a buddy who is much smarter on these things and following your logic, we started at the low end of harness and traced back up to new turn lever. Inside the little switch interrupter the arms were not making contact correctly. We bent them with needle nose pliers and it's working!!!

Now if only I could find the lost key to the door. Spare works in ignition but not door. Small problem comparatively. Thanks again! J