What does a difference of 2 volts between the alternator output terminal and the positive battery terminal indicate?

A 2-volt difference between the alternator output terminal and the positive battery terminal suggests that there is high resistance present in the cables and connections. This high resistance could be due to corrosion, poor contact, or damaged wires, which prevent the full output voltage of the alternator from reaching the battery properly. In a well-functioning electrical system, the alternator should produce a voltage that is very close to the battery voltage, typically between 13.5 to 14.5 volts when the engine is running.

When a significant voltage drop occurs, it indicates that the current is struggling to pass through connections or wiring that are not in optimal condition. This not only affects charging efficiency but could also lead to other electrical failures down the line. Therefore, identifying and rectifying high resistance issues is critical in maintaining the performance and longevity of the electrical system in a truck or coach.