Why Did My Wire Burn Up?

I was driving my Challenger this morning and I wanted to test the parking lights while I drove around just to make sure everything was running good. But less than five minutes with the parking lights on, smoke rolled out of the dash behind the light switch. When I pulled it apart, one of the wires that "I" made burned up. The jacket burned right off of it. The end connections were not scored and a second wire that was attached to the wire was not burned, just the main wire that is only about 4 inches long.
I assumed that I did something wrong when I made it but I am also wondering if the piece of wire that I used could have been the issue. It was just a loose wire that I had in my wire collection.
This wire was attached to my head light switch on the next reply. The second wire (blue) feeds the light bulb on my A/F gauge and that wire was not affected. All of my turn signals still work so it appears to be just the connection at the switch.
What do you think I did wrong?
Thanks

This is where it hooked up.

Too much current for the wire size. A byproduct of current is heat if the gauge is marginal. Too much current, too much heat, hence a meltdown.

Was the new wire for the A/F gauge downstream from the melted wire. If so, you had added the load on the supply wire more than it was design for.

Here are the first few things that come to mind:

1) Those crimp connectors are not the way to make a quality connection but they should handle moderate loads.
2) You used too small of a wire for the load. Remember that all the instrument lights are also carried on the driving light circuit.
3) You failed to use relays to carry the load stated above.
4) There was a short somewhere in the system.
5) You failed to use the proper size fuse in the circuit.

Dean,
I did feed the light bulb off of the switch so that when the lights are turned on, my A/F gauge lights up.
I have already made a second wire assembly and the existing 16 or 18 gauge wire that burned up is now a 14 ga wire. Will this fix it?
I also added a 5a fuse on the blue wire going to the A/F gauge. Is this enough or wrong? My existing head light switch wires are now 14ga and they look fine.

Thanks for the reply.

I think you missed the point.
Unless something is wrong with the A/F gauge adding a 5 amp fuse won't fix your problem.
What size fuse do you have supplying power to that switch? If you had enough draw to burn an 18 gauge wire it's still going to be enough power to make a 14 gauge wire hot. You don't want hot.
You shouldn't have more than 15 amps running through a driving light circuit. If that's the same circuit as your headlamps imagine how quickly that line is going to smoke when you add that much more current.
Put the exterior lights on a relay. It will take a bunch of load off that switch and wire.

My headlights do have relays and I added the fuse to the A/F gauge just in case. Is the fuse needed?
Thanks

Quote:

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My headlights do have relays and I added the fuse to the A/F gauge just in case. Is the fuse needed?
Thanks

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HL power isn't factory fused; it gets battery power via the fuse box on the Batt Buss block. The main power wire (black) at the HL switch is 12awg per factory.

That pic you show; what does it feed besides the aftermarket gauge?