Earthing Kit Test, and reality facts.........
Before you install loads of wires everywhere get a digital multimeter and set it to resistance (ohms), and put the neg (black) onto the neg on your battery then put the positive to as many different locations on your cars body/engine as you can reach, if you get any reading at all other then 0.000 (no resistance) then the kit will help functionality. If all you get is no resistance or all 0s then it wont do bugger all, just make sure you have a really good neg to body connection and a really good neg to engine connection wire and you will be fine. Clean the connection matting surfaces (where the wires touch the body/engine) and use something like electric conducting grease between the mating surfaces and on the bolts thread for maximum surface contact area as a really big gauge wire is only as good as the connection points you have.
If the kit came with a voltage stabilizer, do NOT put that on it will only screw with your cars electrical bits as a cheap ones do not have the ability to regulate correctly, if your really need them say if your voltage was spiking and dipping that much then a new alternator or a rebuilt one would be needed