2. To find amperage: I = E/R3. To find ohms: R = E/IThe Ohm’s law formula is a useful one toremember because it helps in understanding the manythings that occur in an electric circuit. For example, ifthe voltage remains constant. the current flow goesdown if the resistance goes up. This can be betterexplained by using a truck lighting circuit that is goingbad. Suppose the wiring circuit between the batteryand the lights has deteriorated due to connectionsbecoming poor, strands in the wire breaking, andswitch contacts becoming dirty. All of these conditionsreduce the electron path or, in other words, increaseresistance. This increased resistance decreases thecurrent flow with the battery voltage constant (forexample, 12 volts). If the resistance of the circuit whennew was 6 ohms, then 2 amperes will flow. To answerthe equation, 12 (volts) must equal 12 (amperes timesohms). But if the resistance goes up to 8 ohms, only 1.5amperes can flow. The increased resistance cuts downthe current flow and, consequently, the amount oflight.If the resistance stays the same but the voltageincreases, the amperage also increases. This is acondition that might occur if a generator voltageregulator became defective. In such a case, there wouldbe nothing to hold the generator voltage within limits,and the voltage might increase excessively. Thiswould force excessive amounts of current throughvarious circuits and cause serious damage. If too muchcurrent went through the light bulb filaments, forexample, the filaments would overheat and burn out.Also, other electrical devices probably would bedamaged. However, if the voltage is reduced, theamount of current flowing in a circuit will also bereduced if the resistance stays the same.For example with a run-down battery, batteryvoltage will drop excessively with a heavy discharge.When you are trying to start an engine with a run-downbattery, the voltage will drop very low. This voltage isso low that it cannot push enough current through thestarter for effective starting of the engine.CIRCUIT CONFIGURATIONSAutomotive circuits (fig. 1-12). The body andchassis of an automobile are made of steel. This featureis used to eliminate one of the wires from all of theautomobile circuits. By attaching one of the batteryterminals to the body and chassis, you can connect anyelectrical component by hooking up one side, by wire,to the car battery and the other side to the body. Thisdesign of connecting one side of the battery to theFigure 1-12.—Typical automotive circuit.1-10