Backup Light Circuit
This backup light circuit has two connectors. One of them is dropping over 3 volts. This is too much voltage drop and should be inspected further. Sometimes female connectors can become spaded resulting in excessive resistance in the circuit. A loose plug will result in an intermittent connection.
If this plug where loose, the backup lights would flicker on and off or not work at all. If there's intermittent operation in an electrical circuit, inspect all of the connector's included. Loose connections result in damaging excessive heat. This is more evident in high current circuits like the alternator or starter circuit.