Replacing the light switch to the headlamp?

The engineers put a lot of effort into making this as difficult and complicated as possible. The procedure to replace the head lamp switch is shown below.

Besides that, there is something you must do anytime you have a switch or relay with overheated terminals. Those two or more terminals must be identified, then replaced with new terminals in the socket or plug. If that is not done, the blackened terminals will have excessive resistance which translates into heat buildup and a repeat failure. Both the switch and the terminals in the plug must be replaced at the same time.

You can find a replacement plug at any auto parts store, but it will typically have to be ordered, then you have to splice a lot of wires. A faster approach is to cut out the burned terminals from the plug, and cut away the melted part of the plastic. Those wires will have also been overheated and will be hardened for about the first four inches. Solder won't adhere to that, so cut off that four inches, then splice in new pieces of the same diameter. Solder those splices, then seal them with heat-shrink tubing. Don't use electrical tape on a vehicle as it will unravel into a gooey mess on a hot day.

There's two ways to replace the terminals. My preferred method is to use a pair of crimp-style universal spade terminals, but solder them too. Plug the connector onto the switch, then plug in the new terminals through the hole left by cutting away the melted plastic. I like to squeeze those new terminals a little tighter so they make solid contact.

The second method involves harvesting a used plug from a salvage yard and using two terminals out of it along with at least that four inches of wire. That way the terminals are already crimped to the wires so that part is done.

This problem is usually caused by the switching contacts arcing resulting in pitting, a poor contact, then heat buildup. That heat results in more resistance, then more heat, until that heat migrates into the connector terminals. It can also go the other way where the heat buildup occurs between a pair of mating terminals, then transfers into the switch contacts. Either way, both the switch and the affected terminals must be replaced at the same time to prevent a repeat failure.

This is a common failure with heater fan speed switches too as well as any other switch or relay in a high-current circuit.

Let me know how you make out or if you have more questions.