Voltage drop
Will use a long piece if 12g in the morning
It's just probe extension. Any reasonable size will do.
The objective is to measure voltage drop in the positive wiring.
Voltage drops when current flows through resistance.
Current is electrons moving. The current flowing out of the alternator or battery's positive is the same as the current flowing though it's ground connection.
If there is a drop in voltage between the power source and the equipment, then there is resistance to flow in the positive wiring.
If voltage drop to the pump is high, then there is significant resistance. Probe additional locations until its found.
What is high resistance?
That depends, but lets use an easy example.
Say a fuel pump draws 11 amps at 14 Volts, and 10 amps at 12 Volts.
Battery supplying power around 12.5 Volts, we measure a 0.5 Volt drop between the battery and the pump.
V=IR
0.5 Volts = 10 amps x Resistance
0.05 ohms = Resistance
Think about that.
Just 0.1 ohm of resistance will cause a 1 volt drop to our example pump.
