My headlight/parking light switch position has a short. When engaged the 15amp engine side fuse blows. Apparently this circuit controls interior dash lights, cab cargo light, running lights, tail lamps, license plate lights and parking lights. I have replaced headlight switch, checked under dash for obvious burnt wires...none found. Removed dash panel for visual, removed radio...nothing found, Question: will burned out bulbs cause this failure? Checked running lights, cargo light for visual short (burnt wires) nothing visual. Man....this is driving me crazy. Can't drive at night, no dash lights, tail lights, only brake lights. I need help. Any help, any suggestions would greatly be appreciated. Thanks in advance.

 

It's been a while since I've chased down electrical gremlins, but hopefully, someone will come along that can elaborate on what I'm talking about. There is a way, using a multimeter, that you can track down a short in a wire and based on the ohm reading you will know approximately how far from your meter the short is. I know, it's not much, but it's all I can think of in my pre-coffee state.

 

Which fuse is the "engine side fuse" ? The lighting wiring is a bit convoluted, the head lights have their own fuses, then there is a fused feed from the PDC to the interior fuse panel which in turn has fused connections to the interior light, instrument panel etc..

Burnt out bulbs don't cause shorts, at least I've never seen or heard of it.

 

If you only turn the switch to parking, does the fuse blow? If yes, it's in that circuit. If no, blows when you turn to headlight, in that circuit. Do you have a trailer harness? I guess you could disconnect bulbs and see if it blows then. Time consuming but you could narrow down to front or rear.

 

Never heard of this method. But that would be very vague method anyway, as the ohm reading depends on how severe the short is. Now OP has the issue where 15 amp fuse goes instantly(?), meaning ohm reading would be somewhere around 0,0-1,0 ohms.

Best way to find the issue is to isolate circuits. Instead of blowing fuses, multimeter is useful. Set multimeter to beep, place one lead to negative battery terminal, and the other lead in place of the fuse. Not the battery side, but circuit side. Then set the multimeter to beep, and start pulling the wiring. When the beep stops, you are close. Also pulling the bulbs might help. It's rare, but filament in bulb can melt so it doesn't glow, it just burns the fuse. I've found this issue twice, and latest was a weirdest thing ever! It was shuttle type bulb, and that circuit kept blowing fuses. I went though the wiring, didn't find anything. I had taken the bulbs out to chech the holders, they were good. But didn't blow the fuse when the bulbs were out. Installed bulbs as the filaments were not broken, but fuse went once again. Then I looked the bulbs more closely, and noticed that filament on the other bulb looked like more "solid'. Got new bulbs and all good, lights work.
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The head light switch, ........when engaged ONLY to parking lamp position.......the 15amp fuse, located in the engine compartment that services the parking light circuit blows. Dash instrumentation lights (speedometer/tach display) go out, parking lights out, cab running lights out, tail lights out, license plate lights out, and cab cargo light out. One side note,...emergency flashing lights (parking light bulbs) work when that button is depressed, for what that's worth. Replaced head light switch when this first started, due to it got screaming hot.....After that initial occurrence and subsequent head light switch replacement, it became an intermittent condition. Seemed (?) like it would only happen after rain, persistent soaking rain. My thought was/is cargo light, or running lights, .....since it is a 21 yr. old vehicle....maybe these connections have corroded. Have pulled EVERY bulb & checked for continuity......all good. Did visual inspection of wiring and connections at those locations connections....as much as I could...looks good. Did visual inspection of the wiring under the dash looking for anything that looks suspect, melted wiring, burned insulation, presence of tiny electrical gremlins. ....nothing. WTF this is a nightmare. Can't drive at night and out of ideas as to what the hell is going on. Any help suggestions, ideas, rude comments all welcome at this point.

 

Please remove your headlight switch and double-check the switch's connector harness closely. Many times when the switch overheats, it will loosen or melt the terminal connectors that plug into the switch. Aftermarket headlight switches typically supply a new headlight harness with the switch for this very reason. Also, please check the wiring coming into the headlight switch's connector block to ensure they aren't causing your short..

 

This! Is the truck a 2500-3500? How fast after the switch is turned on does the fuse blow?

 

It is a 2002 2nd Gen 2500 5.9l gas spd., quadcab, SB. I've owned it from day one, now with 140,000mi. The 15amp fuse in question, position#19 in fuse panel in engine compartment, blows immediately when light switch is engaged to parking lamp position. Immediately, and it gets warm considering the instant it blows is a fraction of a second. I'm thinking there's got to be a loose ground/failed ground connection somewhere...correct?

 

Failed ground won't normally blow a fuse. Direct short will.