AO Silver Member
Join Date: Mar 2003
It will be electrical and I'd say battery but you can do these checks to find other faults...
Checking the load point for full battery voltage will tell you whether or not sufficient voltage is getting through, and to do that you need a voltmeter. The battery itself should be at least 70 percent charged and read 12.43 volts or higher (12.66 volts is fully charged). If the battery is low, it should be recharged and tested. The output of the charging system should also be checked, and be about 1.5 to 2.0 volts higher than battery base voltage (around 14 to 14-1/2 volts). If the battery is OK, your voltmeter should read within 1 volt of battery voltage at the circuit load point in any given circuit.
Low circuit voltage is usually caused by excessive resistance at some point in the wiring. Usually this means a loose or corroded connector, a faulty switch or relay or poor ground. To find the point of high resistance, use your voltmeter to do a "voltage drop test" at various points throughout the circuit. If the voltmeter shows a drop of more than a 0.4 volts across any connector, switch or ground contact, it means trouble. Ideally, the voltage drop should be no more than 0.1 volts.
If low voltage is detected in a number of circuits, do a voltage drop test across the battery terminals and engine/body ground straps. Loose or corroded battery cables and ground straps are a common cause of voltage-related problems. Clean and tighten the battery cables and/or ground straps, as needed.