Mechanics

BATTERY LIGHT NOT GOING OFF

1994 Ford Ranger • 6 cylinder 2WD Manual • 183,000 miles

I HAVE A 1994 FORD RANGER LIGHT PICK UP TRUCK XL REGULAR CAB 3.0 LITRE ENGINE V 6 AND I RECENTLY CHANGED THE BROKEN ALTERNATOR AND I PUT IN A USED ONE AND NOW MY BATTERY LIGHT WON'T TURN OFF, WHAT IS THE PROBLEM THERE?
NOV. 17 2010
MY E-MAIL ADRESS : EDDMONTON2010@GMAIL. COM
FROM EDMONTON ALBERTA CANADA
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EDDMONTON
November 18, 2010.



Ensure battery is in good condition and fully charged. Connect negative voltmeter lead to negative battery post, and positive voltmeter lead to positive battery post. Record battery voltage. This reading is base voltage.
NO-LOAD TEST
Connect tachometer to engine. Start engine and operate at 1500 RPM with no electrical load (foot off brake and doors closed).
Measure voltage when needle stops moving. This may require waiting a few minutes. Voltmeter reading should increase, but not more than 3 volts greater than base voltage.
If the voltage increases at least.5 volt over base voltage, go to LOAD TEST. If voltage increase is more than 3 volts, proceed to HIGH VOLTAGE TEST. If there is no voltage increase, or voltage increase is less than.5 volt, proceed to LOW VOLTAGE TEST.

LOAD TEST
Connect tachometer to engine. Start engine. Load alternator by switching heater/air conditioner blower motor to high position and headlights to high beam. Increase engine speed to 2000 RPM.
Voltmeter should indicate at least.5 volt more than base voltage under normal operation. If voltmeter indicates high voltage (3 volts greater than base voltage), go to HIGH VOLTAGE TEST. If voltmeter does not indicate at least.5 volt greater than base voltage, go to LOW VOLTAGE TEST.

HIGH VOLTAGE TEST
Set ignition switch to RUN position (engine off). Measure voltage at alternator output connection at starter relay, then at regulator terminal "A" screw head.
A voltage difference between 2 locations, greater than.5 volt, indicates high resistance in circuit "A" wiring. Repair circuit "A" and rerun NO-LOAD TEST and LOAD TEST.
If high voltage condition still exists, inspect alternator and regulator grounding screws for looseness.
Tighten grounding screws, and repeat NO-LOAD TEST and LOAD TEST.

If high voltage condition still exists, connect voltmeter negative lead to ground. Ensure ignition is off. Measure voltage at regulator terminal "A" screw head and then at regulator terminal "F" screw head. Different voltages at 2 screw heads indicates a malfunctioning regulator grounded brush lead or a grounded rotor coil. Replace alternator/regulator assembly.
If same voltage (battery voltage) exists at regulator terminal "A" and terminal "F" screw heads, there is no short to ground through alternator field/brushes. Replace regulator, and repeat NO-LOAD TEST and LOAD TEST.
LOW VOLTAGE TEST
Disconnect wiring harness connector from regulator. Measure resistance at regulator terminal "A" and terminal "F" screw heads. If resistance is greater than 2.4 ohms, go to next step. If resistance is less than 2.4 ohms, replace alternator. Repeat LOAD TEST.
Reconnect wiring harness to regulator. Measure voltage at terminal "A" screw head. If battery voltage exists, go to next step. If battery voltage does not exist, repair terminal "A" circuit wiring. Repeat LOAD TEST.
Ensure ignition is off. Measure voltage at terminal "F" screw head. If battery voltage exists, go to next step. If battery voltage does not exist, repair open field circuit in alternator. Repeat LOAD TEST.
Set ignition switch to RUN position (engine off). Measure voltage at terminal "F" screw head. If voltage is less than 1.5 volts, go to next step. If voltage is greater than 2 volts, go to REGULATOR CIRCUIT "S" TEST. If voltage is 1.5-2.0 volts, replace regulator and repeat LOAD TEST.
Perform LOAD TEST while measuring voltage at alternator output terminal. If voltage increase is more than.5 volt above base voltage, repair wiring harness between alternator output terminal and starter relay battery terminal. If voltage increase is not more than.5 volt above base voltage, go to next step.
Perform LOAD TEST while measuring voltage drop between battery positive terminal and terminal "A" of regulator (with wiring harness connector connected). If voltage drop does not exceed.5 volt, go to next step. If voltage drop exceeds.5 volt, repair wiring harness between alternator regulator and starter relay.
Connect a jumper wire from alternator rear housing to regulator terminal "F" screw.
Perform LOAD TEST while measuring voltage at alternator output terminal. If voltage increase is at least.5 volt greater than base voltage, replace regulator. If voltage increase is not at least.5 volt greater than base voltage, replace alternator.

Unplug wiring harness connector from regulator. Connect jumper wire between regulator terminal "A" and terminal "A" of harness connector. Connect a jumper wire between regulator terminal "F" screw head and ground on alternator rear housing.
Start and idle engine. Measure voltage at terminal "S" and at terminal "I" of wiring harness connector. Voltage at terminal "S" should be approximately half that at terminal "I". If voltages are normal, remove jumper wires. Replace regulator. Repeat LOAD TEST.
If voltage at terminal "S" is not approximately half that at terminal "I", repair faulty wiring circuit or replace alternator. Reconnect regulator harness. Repeat LOAD TEST to confirm repair.

NOTE: Connect voltmeter negative lead to alternator rear housing for all the following voltage readings.

Turn ignition off. Measure voltage at terminal "F" screw head. See Fig. 4. If voltage is less than battery voltage, go to next step. If battery voltage is indicated, system is functioning properly. Further testing is not needed.
Measure voltage at terminal "I" of wiring harness connector. If voltage is zero, go to next step. If voltage is not zero, repair short to voltage in circuit "I".
Measure voltage at terminal "S" of wiring harness connector (with connector connected to regulator). If voltage is not zero, go to next step. If voltage is zero, replace regulator.
Unplug wiring harness connector from regulator. Measure voltage at terminal "S" of harness connector. If voltage is not zero, repair short to voltage in wiring harness. If voltage is zero, replace alternator.

BMRFIXIT
Nov 18, 2010.