Parking lights and side marker lights stay on constantly

[hotrodsinner]

Hoping I can get some help. I have a 71 c10, both my front and rear parking lights and side marker lights stay on constantly. With truck on, truck off, Key out, headlights on or off. No matter what. Just started recently. The only thinks I have done yo it since this issue started was cut out an old trailer light socket that was spliced into the wiring at rear tailights. Also I changed the steering wheel on truck. It has a new light switch. I checked fuses. What would cause this? A bad ground? A hot wire?

[hotrodsinner]

Also I have installed one of those upgraded headlight harness that make the headlights brighter. But that's been in there before this all happened.

[VetteVet]

Start by unplugging the headlight switch Do they go out?

[hotrodsinner]

Originally Posted by VetteVet

Start by unplugging the headlight switch Do they go out?

Unplugged headlight switch and parking lights turn off. Plug switch back in, lights on

[VetteVet]

Pull the stop/tail fuse in the fuse panel and see if the lights go out. If they do then the headlight switch is wrong for the year or more likely it is shorted internally.




With the switch off,and the plug unplugged, test between the red and brown terminals with your multimeter for continuity. If you get zero ohms then the switch is shorted.

[hotrodsinner]

It was the switch! Shorted internally! Thank you VetteVet,

[VetteVet]

Originally Posted by hotrodsinner

It was the switch! Shorted internally! Thank you VetteVet,

Elementary my dear Watson!!!

[D'Monsta]

OK guys.. My marker and tail lights stay on even when the switch is disconnected.. My headlights turn on when I have the key on whether the switch is pulled out or not. Turn key off and headlight go out but markers stay on.. Any ideas?

[dmjlambert]

You didn't say what year your truck is, but if you're talking about something earlier than 1973, there is no connection between key switch and tail lights and headlights. I see in other posts you have a 1966 truck, but I don't know if that's the one you're working on for this electrical problem.

You likely have some customized wiring in your truck, because in a stock truck the key switch has nothing at all to do with headlights or marker/tail lights. Show us a wiring diagram for your truck and somebody could probably give clues about what to look for next. Or you'll have to inspect the wiring and trace the wires and see what devices they go to. My guess is you added a relay (or hired somebody to customize or previous owner customized) to switch off the lighting with the key switch and perhaps have a daytime running light circuit (also something custom or more modern), and one of the relays is bad. It's also possible you have stock wiring but some of it is damaged, and wires are shorted together. On my truck rats ate part of the insulation off of several foot-long strips of wiring that were in the frame rails and inside the front fenders and under the battery, and I had to do some repairs.