My brake lights did not work at all. I had a melted fuse. Fixed, and brake lights work. However, it created other problems. radio not working dome lights not working trunk light not working head lights do not come on when car is not started

2004 Hyundai Elantra a real melt down (or just humor to say battery died as all do often)
most batteries never last 10 years, ever.(my 50y records me)

1. check all fuses first cab and engine bay.
2. check battery voltage running 13 to 15vdc good less is alternator is dead, (3 fuses bad makes new alternators fail too)
3. you never put the battery in backwards right?
4. you never jump started the car jumper cables backwards right?
5. scan the PCM yet, I bet it tells DTC errors, that you missed.
6. PCM means DLC ODB2 16pin port, all USA cars have 96 up.
7. what does melt down mean and doing what? IDK.

Fuse 142, with key on, use a test light and check voltage on that fuse circuit, it should be hot, if not, we'll have to back track. If the fuse melted in fuse box, makes me wonder about fuse box?
You could take the connector loose from brake switch, Use a jumper wire between terminals 1 and 4, provided terminal 1 is hot with key on, the brake lites should work. I can only help with testing. I don't know if brake switch is adjustable?

could have a grounded wire or when you blew the fuse the fuse holder heated up and melted a little and its touching a metal area creating a ground

There will be a short somewhere in the wiring harness, remove and check the brake light bulbs, make sure the holders are ok and not damaged. If they appear ok then the issue will most likely be in the wiring somewhere between the back of the car and the fuse box.

have you checked both fuse boxes, there is one inside the car and one in the engine between your battery and overflow tank, I had some light problems and found that one of the bigger fuses in the engine compartment was melted so make sure you check both spots

Your brake light switch was sticking and now the fuse box is shorted. between those 3 systems. it happened to me in a 90 ford it was wipers brakes and radio. I took fuse box down and taped wires, and replaced brake light switch and it fixed it

check the light switch and harness that plugs into it. my friend has one and we replaced the switch and it fixed it.BE VERY CAREFUL WITH THE HARNESS, THEY HAVE A TENDENCY TO MELT CINCINNATI-ED

You will need to replace the rear light assembly that was melted.

Lok in the trunk on the left side, behind the carpet for a small plastic box with a bunch of wires going to it. Look to see if there is brake light powe coming in with the pedal depressed. If so, and no power is coming out, you need to order and replace the "taillamp failure sensor".

find out what fuse controls. look under dash for burnt wires. let me know what you find.