To check the bad wiring connection, one can do voltage drop test. To do a voltage drop test, one needs to create a load in the circuit that is to be tested. Then use DVM (digital volt meter) to take the readings of the circuit. When the connection is good between the voltmeter and circuit, you will get some readings on the meter. If the readings shows very little or no voltage, then the wiring is perfect in the car. But if you experience high voltage, then the wiring in the car is bad.
If you don't know how to do it, you can directly go to a professional garage, they can do it easily.