TED NEAL'S AUTOMOTIVE TROUBLESHOOTING HELP SITE. I have 35 years experience and my associate, Dave McConnell, has 22 years experience. Let us know what the trouble is and we'll do our best to help you out.

ELECTRICAL TROUBLESHOOTING TIPS To troubleshoot car problems related to electrical components often requires a high degree of skill. It can also be the most frustrating among the myriad of troubleshooting tasks. The diagram of a car's primary 12V electrical system is shown below. It consists of a Battery, and an Alternator which is referred to by the name "generator" and the vehicle's Primary Ground System consisting of an Accessory Ground and an Engine Ground. To get familiar with a vehicle's electrical system in order to troubleshoot it, trace the wires in between all components to see how they connect together. The Battery The vehicle's battery stores electrical energy in chemical form and must deliver large amounts of electrical energy (current) to crank the engine. Many starting problems are caused by battery problems. Troubleshooting the electrical system will quickly reveal this. Identify both battery posts on the battery in the diagram. One post is marked "+" for the positive or "hot" side and has a red or black battery cable connected to it. The Junction Block is a voltage side common connection point used on some vehicles. It is located in the engine compartment near the battery. The negative battery post is marked "-" (minus sign). The negative battery cable is usually a two wire black cable. The smaller diameter cable is connected to the sheet metal for the Accessory Ground. The larger diameter wire is connected to the engine block for the Engine Ground. The Alternator The alternator produces a charging voltage to electrically power the vehicle and recharge the battery as long as the engine is running and the alternator is performing properly. Accessories which don't function are often attributed to a problem with the alternator. Again, troubleshooting the electrical system will reveal this. The positive output terminal of the alternator, called the "B+" terminal, is usually a large insulated terminal on the rear or side of the alternator housing with a heavy gauge wire connecting back to the battery's positive (+) post through the Junction Block. The alternator housing is the alternator's negative (-) terminal. Trace both the positive and negative battery cables from the battery posts to their connection points in the vehicle. Battery "+" goes to Alternator "+" (the B+ terminal) through the wiring harness. Battery "-" goes to Alternator "-" through the engine ground and the engine block. The purpose of the regulator is to excite the alternator and prevent the charging voltage from rising above a preset limit. The regulator may be mounted external to the alternator and bolted to the vehicle's sheet metal with wires connecting to the alternator or it may be mounted inside the alternator. To troubleshoot the primary electrical system requires a digital voltmeter. This will uncover a large number of one's car problems related to electrical components. DMM A diagram of an Autoranging DMM is shown. Note the symbol for the DC Voltage function. It is a small solid line above a small dotted line followed by a "V". This means "DC Volts." By selecting DC Volts, an Autoranging DMM automatically sets to the lowest milli-volt (mV) DC voltage range, usually 400 or 500 mV depending on the DMM. All DMMs display 00.0 or 000.0 when on the milli-volt range so 100 mV (or 0.10V) would read as 100.0 (mV). When an Autoranging DMM senses the test voltage is above the value of the milli-volt range, the DMM automatically steps up to the next higher voltage range which is 2.00, 3.00 or 4.00 V DC range, depending on the DMM brand. All DMMs display .000 on the 2/3/4 volt range so 1.5 volts would read as 1.54 (V) so as to facilitate troubleshooting of the system. When an Autoranging DMM senses the test voltage is above the value of the 2/3/4 Volt range, the DMM automatically steps up to the next higher voltage range which is the 20.00, 30.00 or 40.00 V DC range, depending on the DMM. This is the range the DMM must be since cars run on 12 volt systems and no voltage greater than 20 volts is measured. All DMMs display 1.01 on the 30/40 Volt range so 16.25 volts would read as 14.25 (V). Copyright 2000. Ted Neal, Inc. Please e-mail me if you have any questions about this website or would like to suggest a link. Thank you.