Hi Sorry for late reply was away. General rule of thumb is to have the ignition off when connecting/disconnecting cables. This is because of faults that could occur whilst unplugging particularly if the pins are quite loose in the plug or socket and voltage supply issues could occur. Also when turning the ignition on the system does a wiring self check to check for faults and this will help narrow down the fault area if there were no faults before plugging in. I also recommend having a can of water displacement spray [3m does a good one] to help with connectivity.