Electrical Components - Maintenance
Electrical Maintenance Topics
  1. Battery, Alternator, or Voltage Regulator Problem Diagnosis
  2. What Battery Capacity Is Needed?
  3. Can You Replace A Halogen Headlight With An Ordinary Headlight?
  4. Why Are Returns on Electrical and Electronic Parts Not Accepted?

Battery, Alternator, or Voltage Regulator Problem Diagnosis

Battery keeps running down

Is it the Battery, Alternator, or Voltage Regulator?

It could be any one of the three. It could also be an undetected current drain caused by a trunk light, underhood light, or glovebox light that does not go out when the lid is closed or even a chaffed wire making contact with a metal body part.

Check the battery first
The first thing that should be checked is the battery state of charge. If it has a built-in hydrometer (charge indicator), a green dot means the battery is 65% to 75% charged and okay for use or further testing.

If the charge indicator is dark, the battery is less than 65% charged and needs to be recharged and load tested.

On 1985 and later model Chrysler vehicles, the charge indicator on some batteries also contains a red dot which shows if the battery is less than 50% charged.

Darkened indicator
(With green dot)
Darkened indicator
(No green dot)
Light yellow
bright indicator
May be
jumped started
May be
jumped started
jump start

If the charge indicator is clear or yellow, the level of electrolyte inside the battery has dropped too far to give a reading. It also means the battery will need to be replaced soon. Once water level drops below the top of cell plates, they dry out and lose their ability to hold a charge.

Never attempt to jump start or charge a battery with a low electrolyte level. It may explode.

The state of charge of a sealed top battery without a built-in charge indicator can be determined by measuring its open circuit (no load) voltage:

A low charge level does not mean anything is wrong with the battery or charging system, it simply means the battery is low and needs to be recharged.

The Load Test Is Next
Performing a load test would be the next step. This checks the battery's ability to deliver current. The battery must be at least 65% charged before load testing. If not, a good battery may fail the test.

A conventional load test is performed with a carbon pile battery tester. The load created by the carbon pile is adjusted according to the battery's cold cranking amp (or amp/hour) rating. The carbon pile is usually set to one half the battery's CCA rating (or three times its amp/hour rating).

Temperature compensation is also important because a cold battery puts out fewer amps than a warm one. The load is then applied to the battery for 15 seconds while voltage output is observed. If voltage remains above 9.6 volts, the battery is good. If it drops below 9.6 volts, the battery can be recharged and retested, or given a three-minute charge test.

Sulfated Battery Test
A three-minute charge test checks for a sulfated battery. As a battery discharges, lead sulfate is deposited on its plates. If the battery is not re-charged soon after the discharge, the lead sulfate may harden, preventing proper re-charging later. Sulfation may also result from a battery being in a constant low state of charge, such as a constant drain, a malfunctioning alternator, or a loose belt.

Slow charge the battery at 40 amps for six minutes, then check voltage across the terminals with the charger on. If the voltage is above 15.5 volts, the battery is not accepting a charge. Slow charging for 20 hours can sometimes reverse the sulfated condition, otherwise the battery is junk.

Charging System Next
Charging System DiagramAn alternator is based on the rotation of a magnet inside a fixed-loop conductor. The output circuit and the field circuit make up the automotive charging system.

If the battery check is okay, the next item to check is the charging system. The charging system check determines that the alternator and voltage regulator are working together properly. A properly working system produces a charging voltage around 14 volts at idle with lights and accessories off (refer to a shop manual for exact charging specs).

When the engine is first started, charging voltage should rise quickly to about two volts above base battery voltage, then taper off and level out at the specified voltage.

Exact charging voltage will vary according to battery state of charge, load on vehicle electrical system, and temperature. The lower the temperature, the higher the charging voltage. The higher the temperature, the lower the charging voltage.

On a GM application, for example, accepted voltage charging range is 13.9 to 14.4 volts at 80 degrees F. At 20 degrees F below zero, charging range is 14.9 to 15.8 volts. At 140 degrees F, the charging voltage is 13.0 to 13.6 volts.

Charging output can also be checked with an adjustable carbon pile, voltmeter and ammeter. The carbon pile is attached to the battery and adjusted to obtain maximum voltage output while the engine is running at 2,000 rpm.Charging Output Diagram

Alternator or Voltage Regulator?
If charging voltage is low, the alternator or voltage regulator could be faulty. To find out which component is bad, a procedure called full fielding can be used to bypass the regulator. If the alternator produces the specified voltage or current output after full fielding, the problem is in the regulator (or wiring) not the alternator.

The exact procedure for full fielding an alternator varies from vehicle to vehicle depending on how the alternator is wired. Basically, the regulator is bypassed by connecting a jumper wire between the field (FLD or "F" terminal) and battery positive (BAT) terminal on the alternator.

On older GM applications with Delco integral regulator alternators, inserting the tip of a screwdriver through the D-shaped hole in the back of the alternator full fields the unit.

Either voltage or current output can be compared against manufacturer specs to determine if the alternator is functioning at full capacity. Generally speaking, alternator output should fall within 10 amps or 10% of its rated capacity at 2,000 rpm.

For several reasons, it is important to follow full fielding test procedures exactly. If only one diode or stator winding is bad, for example, the alternator may still make enough electricity at high rpm to keep the battery charged, but not at idle or low speed. The alternator and/or regulator can also be damaged if the wrong test procedure is used.

On Chrysler externally regulated alternators, for example, you do not apply voltage to the "F" terminal. This system is full fielded by grounding the green wire at the regulator connector. On externally regulated Ford alternators, the alternator is full fielded by disconnecting the four-wire connector from the regulator and jumping across the "A" and "F" terminals.

Other Possibilities
If charging output goes up when the regulator is bypassed by full fielding, but otherwise fails to produce voltage, check the regulator for a poor ground. This is especially important on Ford and Chrysler systems. Poor or open wiring connections between alternator and regulator can also cause a charging problem.

A slipping fan belt is one of the most common causes of under charging. A fan belt that holds at idle or low rpm may slip when the alternator is under load. Glazed or burned streaks on the belt are an indication of slipping.

If the battery and charging system are okay and the battery keeps running down, check for a current drain somewhere in the electrical system. To isolate the cause, remove one of the battery cables and connect an amp meter between it and the battery.

A current drain will cause a reading on the meter. Disconnect fuses one by one until the circuit is found that causes the reading to disappear.

On-board electronics such as the computer, an electronic clock, etc., will draw a few milliamps all the time, but should not be enough to run the battery down unless the vehicle is not driven for long periods of time.

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What Battery Capacity Is Needed?

The Standard Recommendation
A battery should have enough amperage capacity to allow reliable cold starting. The standard recommendation is a battery with at least one Cold Cranking Amp (CCA) for every cubic inch of engine displacement (every two inches of displacement for diesel engines).

CCA rating is an indication of a battery's ability to deliver a sustained amp output at a specified temperature. Specifically, it is how many amps a new, fully-charged battery can deliver at 0° F for 30 seconds and still maintain a minimum voltage of 1.2 volts per cell.

A rule of thumb says a vehicle's battery should have a CCA rating equal to or greater than engine displacement in cubic inches. A battery with a 280 CCA rating would be more than adequate for a 135 cubic inch four-cylinder engine, but not big enough for a 350 cubic inch V-8.

The Battery "Amp Wars"
Battery manufacturers have been trying to outdo one another by introducing batteries with higher and higher cold cranking amp ratings. There was a time when a battery with a 550 CCA rating was considered a powerful battery. Now there are batteries with 650, 750, 850, and even up to 1,000 CCA available.

Even though battery manufacturers might say bigger is better, we still contend that for most cases 1 CCA / cubic inch of engine displacement is adequate. You should only consider exceeding 1 CCA / CI for exceptional conditions, such as heavy industrial use or very harsh climates

Notes: If you upgrade to a greater capacity battery, make sure:

  • The physical size of the battery is compatible with the available battery space in the engine compartment.
  • The battery cable gauge can handle the increased current. One often overlooked source of cranking trouble is under capacity battery cables. If the original equipment cables have been replaced with under capacity cables, or the higher capacity battery now exceeds the cable's rated amperage, serious problems can occur. The cables may not be able to deliver the battery's full amp load to the starter, or worse, may overheat and start a fire.

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Can You Replace A Halogen Headlight With An Ordinary Headlight?

Yes, but ...
It is possible to replace a halogen headlight with an ordinary headlight, but only if the halogen headlamp is a sealed beam. Halogen headlights with interchangeable bulbs only accept halogen bulbs. There is a trade-off to consider; ordinary sealed beam headlights cost less than halogen sealed beams, but they are not as bright.

Halogen lights 40% brighter
Halogen lights are about 40% brighter than conventional incandescent lights. Light output is measured in units called lumens, which is a more accurate measure than candlepower. Conventional incandescent bulbs give off 15 to 18 lumens per watt. Halogens produce 20 to 25 lumens per watt, extending average headlight range 200 feet further down the road. Halogen light is whiter, which also aids visibility.

The filament in a halogen bulb is thinner and burns hotter. They are called halogen bulbs because of the gas mixture used to fill the glass; halogen plus krypton, argon and/or nitrogen. The gas mixture conducts heat away from the filament to prevent it from burning out. Halogen helps redeposit microscopic particles of tungsten that boil off the filament back onto the filament. This extends filament life and prevents bulb darkening with age.

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Why Are Returns on Electrical and Electronic Parts Not Accepted?

Too many people have tried to take advantage of the system. Instead of using proper diagnostic procedures, some people (mostly do-it-yourselfers, but also some so-called professionals) resort to trial-and-error parts swapping when they don't know how else to fix an electrical problem. When parts they have installed do not fix their problem, they want to return them and try something else.

Electrical/electronic parts are easily damaged by improper installation or testing. Because electronics are very sensitive to voltage overloads, it does not take much of a voltage spike to ruin a component.

Unplugging a wiring connector while the key is still on can create a momentary voltage surge of hundreds of volts. Crossing up the wrong wires or using the wrong test procedures can also damage sensitive electronics. You have no way of knowing whether or not the part has been used or damaged.

Because of such risks, many jobbers refuse to allow returns on any electronic components. This may seem unfair to some customers, but it protects the next customer who might get a bad part that had been returned.

Most jobbers will allow returns or exchanges on rebuilt starters and alternators if there is a problem with the unit.

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