Handbook 652 Body Electrical Diagnosis Applying Ohm’s Law • If a 20A fuse is blown , we know that a lot of current must have been flowing in the circuit. In order to get a 20A fuse to blow at 12V, there must be very little resistance (0.6Ω) in the circuit. This condition is caused by too many loads connected to the fuse, aftermarket accessories or a possible short-to-ground . Shorts-to-ground provide either no or a very low resistance path to ground before the load, allowing current to flow unregulated. In this case, the resistance of the load has been removed.
(cont.) General Electrical Rules • Current can only flow when there is a complete path between power and ground (or between a higher voltage and a lower voltage). No complete path = open circuit = zero current. • The resistance of the load limits current in the circuit and converts current into work. In a perfect circuit the only resistance would be the load. • Whenever current flows in a circuit, voltage drops (ΔV) will happen. Voltage drops happen anywhere there is resistance. In a series circuit the load with the largest resistance has the greatest voltage drop. In parallel circuits the voltage drop is the same for all branches of the circuit.
• Every circuit uses up all the source voltage. (Total ΔV always equals source voltage.) 36 Technical Training