Hi folks. I'm a brand new member with a question about the side marker lights on my 1977 F350. With the light switch on, and after about 20 seconds, my side marker lamps go out, and then come back on in about another 20 seconds. You can hear a distinct click from behind the dash. Is there a breaker in the headlight switch? Suggestions and comments, please and thanks.
George

 

Usually the lights going on and off happens first with the headlights. This is a sign that the breaker in the headlight switch is bad and the switch needs replaced.

You can also look into adding some relays to your headlights, which will remove the load from the headlight switch, and make your lights brighter. When I get home from work I'll dig up the links to the procedure.

 

Why is it that when the carbon monoxide detector starts beeping, people's first instinct is to assume it's bad, and remove the batteries? Why immediately suspect a safety mechanism is wrong? It's no different here. Not trying to sling you out here, but let's not spend $30 if we don't have to.

If the headlight switch is clicking, the internal breaker is interrupting. That means there's a short downstream and it's doing its job. Inspect the BROWN wire coming from the switch to all four corners of the truck for pinched or frayed insulation. This signal is likely shorted to ground and pulling an over current.

Of course, it is possible that the headlight switch is bad and prematurely interrupting, but there is no reason to immediately suspect the headlight switch is bad and replace it in the absence of any actual troubleshooting.