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Hi folks. I have a beautiful 1951 3100 with all 12 volt wiring that has been fine for 3 years. Out of the blue my 30 amp headlight fuse is blowing out. I replaced it and headlights work fine. I turn lights off and try turn signals and they dont work now. I replaced turn signal fuses and now they work. I turn headlights on again and now fuse is blown again. Everything is nice, neat and tight. What am I missing here? This is almost as fun as getting used to Windows 10. Thanks for any help.
Bodini

Have you traces the wiring? Sounds like you have a short somewhere in the turn signal wiring.

Does it do it when you use both signals, or just one?

Chris

The headlights should not be fused in the first place- - - -they should be on a self-resetting circuit breaker. In a properly wired system, there should be no shared circuitry between the headlights and the turn signals, so either someone has made some massive mistakes when they wired your electrical system, and/or you have two problems happening at once. The most common place the headlight circuit develops problems is the dimmer switch- - - -it carries some heavy current and it's in a very hostile environment down there on the floorboard.
Jerry

"Out of the blue my 30 amp headlight fuse is blowing out."

Where is your headlight fuse located?

Are you using the original light switch?
1948-1953 light switch

Well, maybe I'm not that smart after all. Maybe it's not a headlight fuse. Ignition works fine and truck starts right up but it's the 30 amp fuse in the middle of my fuse board that pops and then headlights/tailights don't work. She does have the original style headlight switch. The turn signal unit is one of those chrome units that strap onto the steering column. I'll take a look at the dimmer switch but she's a fair weather truck and if the roads wet she stays in the garage. Thanks for your responses.

The headlight switch has a breaker built into it.

Is there any way to check the dimmer switch other than clicking it and seeing if high and low work?

Inspect the wires that connect to the dimmer switch for looseness, brittle insulation, corrosion, etc. It appears that someone has misrouted the power wire tp your light switch- - - it should be connected directly to the ammeter, and the built-in circuit breaker in the light switch protects against shorts downstream of the light switch. In case there is an overload, the breaker is supposed to cycle on and off fairly quickly to avoid losing the headlights entirely. If the truck has had any kind of rewiring done, during an older restoration, maybe, it sounds like someone who didn't understand that principle wired the headlights through a fuse that also feeds other circuits. I'd suggest for starters that you wire a circuit directly to the light switch with a 30 amp circuit breaker in the supply line, not a fuse. That will take some load off the fuse that keeps blowing and also give you a safer way to protect the headlight wiring.
Jerry

Have relays been installed in the headlamp circuit? IF so, that might be the source of the wiring error.

I appreciate all your help very much. Hot Rod Lincoln, my Rebel wiring kit has a power wire straight to the light switch. Are you saying run that wire to the original (but 12 volt) gauge and then wire the switch off of the volt gauge?

Finally got around to "fixing" the problem after waking up in the middle of the night with fix it ideas. I called Rebel wiring and they suggested put a new fuse in and then pull the light switch out to park position then headlight position and see where it "pops". It popped on the park position. Rebel then said to disconnect the brown wires to the headlight switch (park, panel and tail lights) and then reconnect one at a time. It popped when I reconnected the parking light wire. So, since I never use my parking lights I said the heck with it and taped off the parking light wire and called it good. Headlights work, Tail lights and turn signals work. Thanks to you that responded and many thanks to Rebel wiring.

OK, you seem to have some Mickey Mouse aftermarket wiring harness that doesn't follow the factory wiring diagram, so I have no idea where the headlight switch power is coming from. The headlight circuit should be powered from a source of battery voltage that is not routed through any type of fuse so there's no way for the lights to lose power for more than a few seconds. That's the reason to use a self-resetting circuit breaker instead of a fuse. Since you've got a voltmeter instead of the original ammeter, the original circuit diagram can't be followed. Far too many people have bought into the fairy tale that ammeters are some kind of fire hazard. This thread is getting far beyond something that can be solved without some hands-on work by someone who fully understands DC electrical systems, and can trace the individual circuits you have.
Jerry

you should figure out what the issue is and fix it

Sounds like your brown wire is shorted to ground. To isolate you may be able to just pull the parking light bulbs out and replace them one at a time to see which blows fuse. Put an ohmmeter between the wire and ground looking for a short. You could also pull the bulbs out one at a time to see when the short goes away. Fix will probably be a lot simpler than finding it. Good luck