New alt and battery still have charging issue

striker911 said:

That is a more easy diagram, thanks. I hooked the wires up the way they should be now and the same thing.

Heres a shot in the dark. What if my dash light bulb was blown out. Could that cause charging system trouble?

Click to expand...

The dash light has a 500 ohm resistor in parallel with the bulb just in case the bulb burns out. The resistor insures that the regulator will know to turn on and supply current to the alternator field windings.

What generation of alternator do you have now?

You can do an entire rewire of a 2 or 3G control circuit in about 10 minutes. It is a simple set of circuits and is simple to test.

If we knew what the regulator's A, S, I values were showing (KOER) while your alternator acts up, it would make it easier to diagnose. We only have what you report to go from. Can you give a synopsis of the vehicle Make, Model and year, what generation of alternator it has, and what exact testing has been done and what the results were?

striker911 said:

Been real busy with work lately and have not had a chance to come up with your answers (above). One thing. In both schematic's you guys showed me they have a light in the dash. My car does not have a light. Does that change anything?

How can I tell if the alt is a 2 or 3g? The car is a 86 gt 5 speed with ac. Not sure what type it should have.

Click to expand...

The dash light should not matter.

A 2G has an external fan on the pulley.
A 3G is internally cooled (no fan on the pulley).

Never, never disconnect an alternator from the battery with the engine running. The resulting voltage spike can damage the car's electronics including the alternator.

Alternator troubleshooting for 86-95 5.0 Mustangs:
Do all of these tests in sequence. Do not skip around. The results of each test depend on the results of the previous tests for correct interpretation.
Changes in wiring for a 3G alternator are in red.

Engine off, ignition off, battery fully charged.
1.) Look for 12 volts at the alternator output. No 12 volts and the dark green fuse link between the orange/black wires and the battery side of the starter solenoid has open circuited.
3G alternator: Look for 12 volts at the stud on the back of the alternator where the 4 gauge power feed wire is bolted.
No voltage and the fuse for the 4 gauge power feed wire is open or there are some loose connections.
2.) Look for 12 volts on the yellow/white wire that is the power feed to the regulator. No 12 volts, and the fuse link for the yellow/white wire has open circuited.

Engine not running, ignition on, battery fully charged.
1.) Alternator warning light should glow. No glow, bulb has burned out or there is a break in the wiring between the regulator plug and the dash. The warning light supplies an exciter voltage that tells the regulator to turn on. There is a 500 ohm resistor in parallel with the warning light so that if the bulb burns out, the regulator still gets the exciter voltage.
Disconnect the D connector with the 3 wires (yellow/white, white/black and green/red) from the voltage regulator. Measure the voltage on the lt green/red wire. It should be 12 volts. No 12 volts and the wire is broken, or the 500 ohm resistor and dash indicator lamp are bad. If the 12 volts is missing, replace the warning lamp. If after replacing the warning lamp, the test fails again, the wiring between the warning lamp and the alternator is faulty. The warning lamp circuit is part of the instrument panel and contains some connectors that may cause problems.

2.) Reconnect the D plug to the alternator
Probe the green/red wire from the rear of the connector and use the battery negative post as a ground. You should see 2.4-2.6 volts. No voltage and the previous tests passed, you have a failed regulator. This is an actual measurement taken from a car with a working electrical system.

Engine running, Ignition on, battery fully charged:
Probe the green/red wire from the rear of the connector and use the battery negative post as a ground. You should see battery voltage minus .25 to 1.0 volt. If the battery voltage measured across the battery is 15.25 volts, you should see 14.50 volts

3.) Familiarize yourself with the following application note from Fluke: See http://assets.fluke.com/appnotes/automotive/beatbook.pdf for help for help troubleshooting voltage drops across connections and components. . You will need to do some voltage drop testing of several of the wires.



How to do the voltage drop testing on the alternator power feed wiring:
Start the car and place a suitable electrical load such as headlights and heater. Begin voltage drop testing with the power out stud on the alternator to the wire lug attached to it. Next, test from the wire lug on the alternator to the stud on the alternator side of the fuse block. Next, test from the alternator side stud of the fuse block to the battery side stud of the fuse block. Then last of all test from the battery side stud of the fuse block to the battery side stud on the starter solenoid.
Any wire or connection that drops more than .25 volts is defective and needs to be cleaned or replaced.

Start looking for these things:
A.) Bad diode(s) in the alternator - one or more diodes have open circuited and are causing the voltage to drop off as load increases. Remove the alternator and bench test it to confirm or deny this as being the problem.
B.) The secondary power ground is between the back of the intake manifold and the driver's side firewall. It is often missing or loose. It supplies ground for the alternator, A/C compressor clutch and other electrical accessories such as the gauges. Do the voltage drop test as shown in the Fluke tech note link. Measure the voltage drop between the alternator frame and the battery negative post. Watch for an increase in drop as the load increases. Use the Fluke voltage drop figures as guidelines for your decisions.
C.) Bad regulator that does not increase field current as load increases. Remove the alternator and bench test it to confirm or deny this as being the problem.
D.) Bad sense wire - open circuit in sense wiring or high resistance. The yellow/white wire is the voltage sense and power for the field. There is a fuse link embedded in the wiring where it connects to the black/orange wiring that can open up and cause problems. Disconnect the battery negative cable from the battery: this will keep you from making sparks when you do the next step. Then disconnect the yellow/white wire at the alternator and the green fuse link at the starter solenoid/starter relay. Measure the resistance between the alternator end of the yellow/white wire and the green fuse link: you should see less than 1 ohm. Reconnect all the wires when you have completed this step.

I don't think you quite found the solution yet.

The drop in voltage in that wire is due to the resistance in the circuit (the dash light or the ~500 Ohm resistor). The resistor noted is not an ignition ballast resistor.

The resistor may be available from Radio Shack. It is a 500 ohm, 1/2 watt resistor. The nearest common value is 560 ohms, which sould be close enough to work.

Does the 86 5.0L even come equipped with a alternator warning light? My info has a notation that the warning light was only on the 4cyl turbo.The 5.0L shows an ammeter. I also show only four wires on the 86 charge circuit. Two BK/O on the alternator connected to the B+ terminals. Two wires on the regulator. The Y/W is connected to the 'A' terminal and the LG/R is connected to the 'S' terminal on the regulator. There is no stator jumper between the two plugs and there is no connection on the 'I' terminal which would be for the indicator circuit.