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You are here: Home Tech Articles & Tutorials Interior / Electrical Charging System Troubleshooting
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Charging System Troubleshooting


     The charging system on your Ford truck performs two basic functions:

1. Maintains the battery's state of charge
2. Provides power for all of the truck's electrical systems while the engine is running

     It's a fairly simple system, consisting of a battery, alternator, voltage regulator, indicator gauge or warning light, and the wiring that connects the components to each other and to the components they serve.


     It is very important to regularly check the alternator drive belt; this can be done whenever the cooling system is serviced. Check the belt tension using a belt tension gauge. And while both "new" and "old" belt tension specs are provided in your service manual, keep in mind that a belt is considered old after just 10 minutes of use! If you do not have a belt tension gauge, press down on the belt with your thumb midway between the two pulleys. If it deflects more than 1/2", it is too loose.

     The belt should be inspected for signs of wear. Check for oil, grease or hard glaze on the underside of the belt; any of these can cause it to slip on its pulleys, resulting in reduced output from the alternator. Another sign of a worn belt is a squealing noise. (This sound can also mean that the alternator is developing a bearing problem.) To find the source of the squeal, apply aerosol belt dressing to the belt. If the squealing stops or changes pitch, the belt is the source of the noise. If the noise continues as before, remove the belt and run the engine. If the noise is gone, the problem is inside the alternator; otherwise, the source of the noise is outside the charging system.

NOTE: A good rule of thumb is to replace the alternator drive belt every three years, regardless of its appearance.


     It's usually easy to know when the charging system isn't generating enough power -- just look at the warning light or gauge. If the light or gauge is not working, the battery will discharge to alert you of a potential problem. The charging system should also be checked if the engine cranks slowly or if dim headlights brighten upon acceleration.

     A problem that is not as easy to diagnose is overcharging, which occurs when the voltage regulator fails to limit alternator output. This causes the alternator to overcharge the battery, which in turn can ruin the components that use electricity. Also the sulfuric acid battery fluid vaporizes at a faster rate when too much current is being supplied. If the battery cells are allowed to empty, the dry plates will deteriorate and the battery will die. It is even possible for an overcharged battery to explode.

     For this reason, the battery fluid level should be checked very few weeks. If the level is frequently low, the system is probably overcharging. Also, check the level immediately if you should small "rotten eggs", which can be caused by vaporized sulfuric acid.

     An overcharging condition can be detected with an ammeter, though a voltmeter is much easier to use. If the ammeter shows continuously high charge rates or of the battery voltage often exceeds 14.5 volts, overcharging is the probable cause.


     The troubleshooting procedures that follow will help you head off charging system problems before they occur. Be sure to do each procedure in its entirety; do not skip any steps.


1. Connect the positive lead of the voltmeter to the positive terminal of the battery and the negative lead to the negative terminal.
NOTE: Protect your eyes with safety glasses or goggles when doing this procedure.
2. Remove the coil cable from the distributor cap
3. Ground the coil cable to the engine block by connecting a jumper cable between the two. This will prevent dangerous arcing of the high-voltage spark.
4. While cranking the engine, observe the voltage reading. It should be above 9.6 volts for conventional batteries and above 10 volts for maintenance-free batteries.

NOTE: A hydrometer can be used in place of this voltmeter test to check battery capacity. Be sure the hydrometer is clean, inside and out, to ensure an accurate reading.


     There are several ways to test a battery to see how good it is. The quickest and easiest is the load test. A predetermined load is placed across the battery terminals and held for ten seconds. At the end of the ten seconds the voltage across the terminals is measured and this voltage determines how good the battery is. If the voltage stays above 11 volts, the battery is good and healthy. If the voltage drops between 9 and 11 volts, the battery is determined to be borderline. It will be okay in warm weather, but may fail as the temperature drops toward freezing. If the voltage drops below 9 volts, it's no good.

     The way we test the batteries state of charge is with a battery hydrometer. A hydrometer measures the specific gravity of the acid solution. The higher the specific gravity, the more charge in the battery. A fully charged battery will have a specific gravity of 1.280 -1.260.

Temperature Compensation Table
Open Circuit Voltage Approximate State-of-Charge at 80F (26.7C) Hydrometer Average Cell Specific Gravity Electrolyte Freeze Point
12.65 100% 1.265 -77F(-67C)
12.45 75% 1.225 -35F(-37C)
12.24 50% 1.190 -10F(-23C)
12.06 25% 1.155 15F(-9C)
11.89 or less DISCHARGED 1.120 or less 20F(-7C)

When you check the battery, you need to check each cell. All six cells must have the same specific gravity. If five cells test at 12.75 and one tests at 12.25, you have may have a bad cell. Charge the battery for about 30 minutes and test again. If the low cell does not come up, it's bad and you need a new battery. Some variance is allowed between cells but if it is a large variance, you may have battery problems.

     The individual cells can also be tested with a voltmeter. Take a coat hanger and make two lead extensions about six inches long and attach them to the meters test leads. Touch the positive lead to the positive terminal and stick the negative lead inside the cell next to it. It should read about 2.1 to 2.3 volts. Now insert the positive lead in the first cell and the negative lead in the second cell. Proceed down the line until you get to the last cell. Here you will put the positive lead in the last cell and the negative lead on the negative terminal. All the cells should read the same, or within 0.2 volts. If one reads 4.0 or more, you have a shorted cell and the battery is no good. If you get a very low reading or a zero reading, the cell is open and again the battery is no good.

     Before you do any battery testing, you need to start with a fully charged battery. If it is not fully charged, then any test results you get mean nothing. So always check the specific gravity before you do anything. Also make sure the terminals are clean and tight.

     Now some batteries are sealed so you can't do a cell test or check the specific gravity. In this case all you can do is charge the battery for about 30 minutes and do the load test. You can also measure the Open Circuit Voltage across the battery terminals with a digital voltmeter. This is the only way you can determine the State-of-Charge. In sealed batteries you will usually see the "green eye" or "magic eye". This a built in hydrometer which only measures the State-of-Charge in ONE of its six cells. Don't trust it. I have seen hundreds of bad batteries with green eyes telling me they are good.


     This test will determine whether or not the system is charging the battery and, if not, whether the alternator or regulator is at fault. It requires a voltmeter capable of measuring at least 16 volts, down to tenths of a volt.

     If the charging system on your car has an external regulator, warm up the engine before performing the following test:

1. Turn off the engine, lights, and all other accessories.
2. Attach an engine tachometer according to the manufacturer's instructions.
3. Connect the voltmeter to the battery by attaching the positive lead to the positive terminal and the negative lead to the negative terminal.
4. Note the voltmeter reading. If you get a reading of 12.30 volts or less, with all known current drains (including lights, ignition and accessories) shut off, the battery's state of charge is at 50% capacity or lower. This indicates poor electrical connections, weak alternator output, excessive current drain from accessories or a defective battery. If it is less than 12 volts, charge the battery. Then note the voltage reading again and record it.
5. Start the engine and slowly increase the speed to 1,500 RPM
6. Note the voltmeter reading again. If it exceeds the engine-off voltage by more than 2 volts, the system has a faulty regulator, a poor regulator ground, or a short circuit in the wiring between the alternator and regulator.
7. If this voltage reading exceeds the engine-off voltage by less than 2 volts, perform a load test. This procedure will be detailed momentarily.

     With current flowing toward the battery, voltage should read 14.8 volts or higher, depending upon the parameters of the voltage regulator. If you see no increase in voltage from your static battery test level, the alternator or regulator is not performing properly. Before condemning these expensive parts, however, troubleshoot further.

     Shut the engine off and leave the meter set for the 12V range. Touch the heavy (BATTERY or BAT) lead at the rear of the alternator with the positive probe. Using a quality engine ground for the negative probe, again read available voltage at the alternator. This should be approximately the same as the battery's voltage reading.

     If you cannot read voltage here, a wiring or fusible link problem exists. Zero the meter and set for DC and K-Ohms. Check the wire from the starter solenoid to the BAT connection on the alternator for continuity and conductivity by holding a probe at each end of the wire. If no opens or shorts exist, the meter will rest happily at the zero line. If there is too much resistance, as with a slight open in the lead or a poor connection, the needle will read upward on the scale. An actual open in the wire prevents the needle from registering at all. Resistance readings help locate corrosion within wire leads, too. Battery cables or terminal clamp connections often develop such problems. Unseen in a visual inspection, a current blockage cannot fool your ohmmeter. The force necessary to keep current flowing is measurable.


1. Keep the tachometer and voltmeter connected as they were for a no-load test.
2. Note and record the voltage reading.
3. Start the engine and turn on the heater (or air conditioner) at high speed. Turn on all lights and accessories.
4. Increase the engine speed to 3,000 RPM and note the voltmeter reading.
5. If this reading exceeds the engine-off voltage by 1/2 volt or more, the charging system is functioning properly.
6. If this reading exceeds the engine-off voltage by less than 1/2 volt, perform a full-field test.


     When the regulator's control function is bypassed, the alternator runs full-field. The method of bypassing the regulator differs, depending on the vehicle. For this reason, please note that Step 1 below of the full-field test is for Ford models only. The remaining steps are the same for all makes.

1. Turn off the engine and remove the voltage regulator connector. Connect a jumper wire between the "A" and "F" terminals of the plug, as shown at right.
2. Once the regulator has been bypassed, repeat the load test.
3. If the full-field voltage exceeds the engine-off voltage by 1/2 volt or more, the regulator is defective and must be replaced.
4. If the increase in the voltage is less than 1/2 volts, either the alternator or wiring is faulty.
5. Inspect the wiring for signs of wear or heat damage. If the wiring looks good, the alternator is probably the faulty component.

     NOTE: When performing the no-load, load, and full-field tests on a vehicle with a catalytic converter, try to finish them within a total engine running time of 5 minutes. If more time is needed to finish the tests, wait 30 minutes before continuing. This will allow the catalytic converter to cool, thus preventing it from being damaged.


     Once it has been determined that the problem is with the regulator and not the alternator, you can find out if the source is the regulator itself or its wiring or ground.

1. Check the wiring between the regulator and alternator for heat damage or wear. (The regulator is mounted on the inner-right-side of the radiator support.)
2. Remove the bolts from the voltage regulator. Use sandpaper to clean off the area around the bolts and the spot where the voltage regulator mounts on the truck. This will assure a good ground.
3. Clean, reinstall and tighten the bolts.
4. Perform all the troubleshooting procedures again to see if the problem still exists. If so, the problem is either with the wiring or the regulator itself. If you have already inspected the wiring, try replacing the regulator.

CAUTION: The battery ground cable should be disconnected before replacing the voltage regulator.


     When the alternator is defective, your shop manual will provide test information and overhaul procedures. Any concern about alternator output should begin with checking the drive belt tension. Next, inspect all wire connections. To test the alternator and regulator output, test the current flow from the alternator with an induction ammeter. Compare the ammeter flow to the OEM specifications for your truck, beginning at an idle, then 1500 RPM, and then finally 2000 RPM. An induction ammeter, although not as accurate as more expensive test equipment, provides a quick sense for alternator output. Since the meter simply fits over the cable or wire insulation, you can test without removing any electrical component.

NOTE: Perform the induction meter test with the battery charge low. You want the alternator nears its maximum output.

NOTE: NEVER disconnect battery with engine running!

     If starter and alternator circuits check okay and the battery's cells read normal specific gravity at a full charge (applicable for open-cell batteries), the chronic low battery voltage is still possible. Accessories like the clock or the improper hook-up of an aftermarket sound system can cause the battery to go dead. (Be sure to wire you sound system through a fused and ignition-switched accessories (ACC) source.)

     A defect in the ignition switch, air conditioning clutch, lighting equipment, the turn signal switch, a radio/tape deck or hazard lamp can each draw excessive current from the battery. The dome, underhood and hazard lamps operate without the ignition switch on, so check these areas first. When an aftermarket accessory taps directly into a battery source, disconnect the accessory and see if the problems resolves.

     If a current drain persists, suspect the ignition switch. A shorted ignition switch can deliver current, even with the key is in the off position. Current may be passing to the coil (or ignition module, if so equipped). You can confirm current flow at each of these areas by taking voltage readings with your VOM.


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