Overview

It's also worth checking out your mainboard's terminal blocks for any melting action. An example can be found here: https://www.reddit.com/r/ender3/comments/cibwbf/heated_bed_screw_terminal_melted_again/

The Ender 3's wires are usually tinned at the end, and there is a decent amount of internet debate on whether or not this is good/bad. However, from what I've seen here, folks who do have a melted terminal block consistently left the tinned wires from the factory installed.

The solution to this problem is to cut off the tinned portion and either install the wires back as bare copper wires, or crimping ferrules onto the end of the wires. A brief set of instructions can be found below.

Some more reading:

1. https://www.reddit.com/r/ender3/comments/gh6m2t/i_need_a_bit_help_im_currently_building_a/fq6r0rm?utm_source=share&utm_medium=web2x
2. https://www.reddit.com/r/ender3/comments/b3smsj/ender_3_a_beginner_guide_on_security_mods_and/

Bare copper wires

Pretty straightforward to do and doesn't require any additional hardware. Post-installation, it's unlikely to happen, but be careful with moving the wires around in case you break the wires inside the terminal block.

1. Unscrew the terminal screw holding the wire in place
2. Remove the wire
3. Cut off the tinned portion
4. Expose more of the copper wire by using either wire strippers or the flush cutters that came with your printer.
5. Twist the copper wires together
6. Install back in to the terminal block
7. Tighten the screw terminal until you can no longer pull the wire out with a light tug, but don't go strong-arming the screw down though!

Ferrules

A 'better' solution would be to use ferrules like this kit: https://smile.amazon.com/gp/product/B07K17VDF2/

These ferrules are designed for attaching wires into screw terminals, but the non-ferrule solution is still better than the tinned wires. I went with the ferrule route just to be safe, and used the kit I linked above. You can substitute this kit with any other kit!

Album with more pictures

Installation is similar to the easy method except it deviates from step 4.

After exposing some copper wire, you want to find the ferrule size that lets you fairly easily feed all the wires into, but also have the least amount of empty space. If you use too large of a ferrule, then the wires can be too loose and likely won't be a good crimp. Additionally, you want amount of the exposed wire to be roughly the length of the silver barrel of the ferrule. It's fine if it's a little too long, as you can use flush cutters to clean up after you crimp the connector.

Each color is suited for a different gauge. Ideally, you would use the ferrule that is sized for your wire. I settled on the following:

1. PSU +/- = Larger gray ferrule (4.0mm^2 - E4009 - 12AWG)
2. Fan +/- = Small white ferrule (0.5mm^2 - E0508 - 22AWG)
3. Bed +/- = Blue ferrule (2.5mm^2 - E2508 - 14AWG)
4. Hotend +/- = Small gray ferrule (0.75mm^2 - E7508 - 20AWG)

Basic steps:

1. Feed the copper cables into the ferrule (make sure all the wires fit inside the barrel!).
2. Use the included ferrule crimper to crimp the ferrule.
3. Assuming all goes right, the wires should be tightly packed inside a rectangular ferrule now. You can give the crimp a little tug and it shouldn't come off.
4. If you exposed a bit too much wire, cut off any excess copper wires at the tip of the ferrule wire flush cutters.
5. Install back into the screw terminal.
6. Tighten down terminal screws. Unlike the bare copper wires, because we used ferrules, we can crank down on the terminal screws until it's nice and snug.
7. Done!

Here's an example video showing how to do all this: https://youtu.be/sMFFzpzKhFg?t=443