1986 Ford F-150 Alternator Problems

Tiny
PBRJUNKIE
  • MEMBER
  • 1986 FORD F-150
  • V8
  • 2WD
  • MANUAL
  • 127,000 MILES
The alternator in the truck was giving me problems (gauge needle was bouncing back and forth, headlights were dimming/flashing, checking with voltmeter showed an inconsistent flow of power would spike to 14 then down to 11 then back to 14. I took the alternator to Auto Zone and they tested it and said it was bad. I purchased and installed a new alternator but when I checked it with a voltmeter it did not appear to be charging. I took the alternator back and had it tested and it passed. I was told to replace one of the plugs (3 wire plug that goes to the stator) I replaced the plug but still no output. I have since noticed that there is a wire broken off near the fender well, I traced that wire back to it's source and it goes to the 3 wire plug I replaced. I don't believe this wire is the reason for the lack of output on the alternator because it looks like it's been broken off for some time. Any ideas on what this problem could be? Thank you in advance for any help you may be able to provide.
Do you
have the same problem?
Yes
No
Monday, February 23rd, 2009 AT 11:21 AM

5 Replies

Tiny
DAVE H
  • EXPERT
What color is the wire and what size of engine is the vehicle 5.0L / 7.3L?
Was this
answer
helpful?
Yes
No
Monday, February 23rd, 2009 AT 11:45 AM
Tiny
PBRJUNKIE
  • MEMBER
The engine is a 302 and the mystery wire is white with a black stripe.
Was this
answer
helpful?
Yes
No
+1
Monday, February 23rd, 2009 AT 12:33 PM
Tiny
DAVE H
  • EXPERT


http://www.2carpros.com/forum/automotive_pictures/266999_150_1.jpg



http://www.2carpros.com/forum/automotive_pictures/266999_1502_1.jpg

Was this
answer
helpful?
Yes
No
Monday, February 23rd, 2009 AT 1:21 PM
Tiny
PBRJUNKIE
  • MEMBER
According to the picture the wire jumps over to the regulator but on the truck it runs back up the wiring harness at least a couple feet before it's broken off. I don't understand why it would run back up that far just to come back to the alternator. Do you think this wire would keep the alternator from outputting power? I also checked that wire with the engine running and it was carrying about 1.05 volts. Thanks for the quick response.
Was this
answer
helpful?
Yes
No
Monday, February 23rd, 2009 AT 1:41 PM
Tiny
DAVE H
  • EXPERT
On all F150 models this wire is looped back to the stator/volt regulator ..


http://www.2carpros.com/forum/automotive_pictures/266999_volt_2.jpg



REGULATOR CIRCUIT TESTS
"S" Circuit With Ammeter
Connect positive voltmeter lead to regulator wiring plug "S" terminal position. Turn ignition on.
Voltmeter should indicate battery voltage. If there is no voltage, "S" wire lead from ignition switch is open. Repair and retest system.
"S" & "I" Circuit With Indicator Light
Disconnect regulator wiring plug, and install a jumper wire between "A" and "F" terminals. With engine idling, connect negative lead of voltmeter to ground. Connect positive voltmeter lead to "S" and then to "I" terminals of regulator wiring plug.
Voltage of "S" circuit should be 1/2 that of "I" circuit. If circuit tests are correct, install a new regulator. Remove jumper wire from regulator wiring plug. Connect plug to regulator and repeat CHARGING SYSTEM TESTING.
DIODE TEST (ON VEHICLE)
Disconnect electric choke (if equipped) and voltage regulator plug. Connect jumper wire between "A" and "F" terminals of voltage regulator wiring plug. Connect voltmeter to battery posts. Start and run engine at idle speed. Record voltmeter reading.
Move positive voltmeter lead to "S" terminal of alternator and note voltmeter reading. If meter reads 1/2 of battery voltage, alternator has an open positive diode. If meter reads about 1.0-1.5 volts more than 1/2 battery voltage, alternator has an open negative diode. Reconnect electric choke into circuit after test is completed.
UNDER VOLTAGE & FIELD CIRCUIT TESTS
To determine if jumping procedure is safe, field circuit should be checked with regulator wiring plug disconnected and ohmmeter connected from "F" terminal of wiring plug to battery ground. Ohmmeter should indicate 3-250 ohms. See Fig. 3 .
If load voltage did not increase 1/2 volt above base voltage, connect a jumper wire across "A" and "F" terminals of wiring plug and repeat test procedures.
If voltage is still under base voltage, remove jumper wire from wiring plug and leave plug disconnected from regulator. Connect jumper wire to "FLD" and "BAT" terminals on alternator and repeat test. If voltage increases 1/2 volt above battery voltage, repair wiring harness or replace regulator.
If low voltage is still indicated, stop engine. Move positive voltmeter lead to "BAT" terminal. If voltmeter now reads base voltage, repair alternator. If voltmeter reads zero volts, repair "BAT" wire or replace fusible link.
Was this
answer
helpful?
Yes
No
Monday, February 23rd, 2009 AT 3:26 PM

Please login or register to post a reply.

Recommended Guides