[OneAdam12]

I replaced the 6v battery with a 12v but when I turn the car on and moved in any direction, it just pushed forward at full speed and stopped taking RC input.

I assume it's too much voltage for the RC module, can I some how separate it? I am not sure about how to do that. There are tons of wires, some are for the lights and speakers.

Here is the wiring under the seat.

[TinCanTomCat]

It won't be trivial if you're not sure, but if you get some pictures of the PCB (without the case) top and bottom, I can probably tell you what you need to modify.

The modification would require buying a part (ideally a buck convertor - £/$ 1-2), setting it (requires a multi-meter), cutting some PCB tracks and soldering.

Basically, it would be separating the logic power and placing the convertor in-between to keep that at 6v, allowing the rest of the circuit to stay at 12v+.
It would also mean that a 16/18v upgrade later would mean no other changes.