To properly turn over the engine, the starter requires a very high current output from your car's 12V battery. Hence, that's why the cable that supplies current from the battery to the starter is incredibly thick and is rated at a higher gauge than most other cables. Here, there are two primary wiring connections. First off, there's the negative cable, which serves as a ground. The negative cable connects the battery's negative terminal to the engine block or the transmission case, near the starter. Then, there's the positive cable, which connects the battery's positive terminal to the starter solenoid. If there are any issues anywhere between the wiring here, such as a faulty connector, it would compromise the ability of the starter to function.