How to deal with the high current flowing into your wires?
As said already you need to take a step back and start learning basic DC electronics and some automotive electrical.

Typically in a car for example you are switching remotely a relay or solenoid on and off. This means large wires don't have to detour through the cab (shorter runs so less voltage drop) and you can use smaller more intricate switches among other benefits.

Think of your headlight switch on your dash or indicator stalk, this then triggers a relay under the bonnet. So the loom to power your headlights just has to travel from battery to fuse box and relay then on to your headlights.

Another problem will be protection of wiring. Not sure if they use the chassis of a go kart like in a car and bond it to the negative terminal but if they do there is potential for shorting on the frame or each other due to wires chafing, rubbing, melting and so on. So you will need to know how to select the right gauge of wiring and protection for the wiring, typically a fuse and where to locate it.

Lastly, how is the motor actually driving the go kart?

I am no expert on motors by any means but is it direct drive by a chain or belt ?

How are you going to do 'throttle' and control the rpm of the motor ?

Unless you are purely asking about a manual on/off switch ?

Any gearing, transfer case or clutch of some sort ?

Are you going to want to do regenerative braking, have the motor brake dynamically or just free wheel?

Motor driving one way or capable of reverse ?

How are you going to monitor charge and battery status ?

Sounds like a microcontroller or similar could be handy ?

Even if you only want this at the back I would imagine you may need a kill switch accessible to the driver up front?

You need to flesh this out more.