Not charging

Gunny87

Active Member
Nov 29, 2015
50
7
28
Murray Utah
Yesterday I install an Auto meter wide band 02 in my 87 GT I also changed the ECU to a Microsquirt a few weeks ago and I figured the wide band would help in getting the tune dialed in, the install went good, first I just hooked it up without hooking up to the MS and drove it around a bit and 02 worked perfect, then came back and tied it into the MS, took it out for a run and it started to lean out the engine really bad and running worse and worse so got it home and returned the tune back to where it was before and tied it in to the MS then it ran fine again, but as I took it out for another run I notice that it wasn't charging? everything works, lights, AC, electric fan, the 02 sensor...... just not charging, confirmed with my multimeter, I converted to the LMR 3g alternator with the 4 gauge wire several years ago and has worked great, so today I pulled the alternator off and took it to O'Reilly's and had it tested but it checked out good so went back home and started looking at the wiring and all I found was the main power line going to the 30 amp relay I added, the relay it self, and the power wire going to the fan were all melted, but the fan still worked. so I fixed all of that, then cut apart the harness were it plugs into the alt. and that all looked good , checked all the fusible links over by the starter solenoid nothing burnt or crusty? nothing else was changed so I'm kinda baffled? I searched on here and found write ups on how to diagnose charging issues and it long and complicated but I'm sure it would help me find the problem but honestly I don't have that kind of time to dedicate to fixing this so that being said....
Is there one of the wires that goes to the alt that triggers it to work and if so which one is it and I will check that tomorrow when I get home from work to see if it's getting power and if not I can trace it back to the source and perhaps see what the problem is
 
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this is the wiring and relay that I found burnt and replaced , neither the fuse in the relay or the the one I put inline where I attached it to the battery didn't
blow
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Alternator troubleshooting for 86-93 5.0 Mustangs:

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.



Revised 28-Nov-2018 to add warning that the instrument cluster must be in place and working for the alternator to charge

Red color text applies to cars with a 3G alternator.

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.

Simple first step: Remove the alternator and take it to your local auto parts store. They can bench test it for free.


Use a safety pin to pierce and probe the insulated connectors from the rear when doing tests with the connector plugged into its' mating connector.

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 off, ignition on, battery fully charged:
1.) The alternator MUST have the instrument cluster in place and working properly. The alternator warning light is a part of the charging circuit. The alternator warning light should glow. No glow, bulb has burned out or there is a break or bad connection in the wiring between the regulator plug and the instrument cluster. 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 voltage regulator. This is an actual measurement taken from a car with a working electrical system. If you see full or almost full12 volts, the regulator has failed.

Engine on, 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 measured across the battery is 15.25 volts, you should see 14.50 volts

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. .


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You will need to do some voltage drop testing of several of the wires.

Start looking for these things:
1.) 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.

2.) 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.

3.) 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.

4.) 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.

5.) Bad power feed wiring from the alternator. Use caution in the next step, since you will need to do it with everything powered up and the engine running. You are going to do the Fluke voltage drop tests on the power feed wiring, fuse links and associated parts. Connect one DMM lead to the battery side of the starter solenoid/starter relay. Carefully probe the backside of the black/orange wire connector where it plugs into the alternator. With the engine off, you should see very little voltage. Start the engine and increase the load on the electrical system. Watch for an increase in drop as the load increases. Use the Fluke voltage drop figures as guidelines for your decisions.


Alternator wiring diagram for 87-93 Mustangs.
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The following are diagrams courtesy of Tmoss & Stang&2birds

Alternator wiring diagram for 94-95 Mustangs.
Mustang-94-95-Alt.gif


Voltage drops should not exceed the following:
200 mV Wire or cable
300 mV Switch
100 mV Ground
0 mV to <50 mV Sensor Connections
0.0V bolt together connections

Alternator wiring circuit
Notice the green wire connects to a switched power source. The circuit contains a 500 ohm resistor in series between the switched power and the alternator. Connecting it to switched power keeps the regulator from drawing current when the engine is not running. The resistor limits the current flowing through the wire so that a fuse isn't needed if the wire shorts to ground.

Also notice the sense wire connects to the starter solenoid and it is fused. It connects to the starter solenoid so that it can "sense" the voltage drop across the output wiring from the alternator.


Fuse link for 86-93 Mustangs
Replacement parts:
14 gauge fuse link for stock alternator.

Bussman BP/FL14 Fusible link
AutoZone

Dorman - Conduct-Tite 14 Gauge Fusible Link Wire Part No. 85620
Advance auto parts #85620
Pep Boys - SKU #8637594
 
Still fighting this!
what I know so far
Charge light not coming on, I've made sure it has a good (tested good) bulb, looked at the little diode and it looks fine, hooked the light in the socket to power with alligator clips and light comes on.
checked power at the connector where it plugs into the cluster which is pin 6 on my 87 and no power
All tested with key on engine off

no blown fuses and all accessories work, lights (except fog lights and this is new for them not working), brake lights, horn, wipers. turn signals, AC clutch, blower fan, even door chime, but one other thing that's new is the check oil light stays on and it's not low on oil? all gauges work including the wide band 02 that I had just installed before all this began, car starts and runs fine except for not charging.

battery voltage at main power lug at back of alt. also same at yellow/white wire
of course no voltage at green/red with key on engine off
I stripped the entire harness down from the alt to the starter solenoid and all looked good no brakes or burns and I now know where the green/red wire hooks in at a plug just below the starter solenoid and then joins into the main harness that goes in through the fire wall.
all fuse able links look good.

took the alternator back to a different O'Reilly's and had it check again just to make sure and it passed again (see pic)

So this has to be in-between that plug just below the starter solenoid and from what I can gather the ignition switch which is where the power for the exciter wire starts??? which is all in a very inaccessible area!
I'm getting frustrated with this!!!

Is there a fuse or fused link that this exciter wire runs through that's between that plug and the ignition switch?

I'm sure once I find the problem it will be something simple and stupid but right now this is driving me CRAZY!!
any ideas would be so appreciated!
 

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@Gunny87


Gunny87
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See http://www.stangnet.com/tech/cluster87-93.pdf for information on the cluster connections and wiring differences between model years. The clusters are interchangeable, but you have to do some trimming & move some wires.
You will need the Adobe Acrobat viewer which is also a free download – http://get.adobe.com/reader/

There is no fuse or fuel link between the instrument cluster and the D shaped plug on the back of the alternator.

Disconnect the D shaped plug from the back of the alternator and use a paper clip and jumper wire to ground the red/green wire to the alternator housing or engine block.

Remove the instrument cluster to gain access to the wiring connectors on the back of it. Look for the red/green wire on the connectors and then measure the resistance between it and chassis ground using the Low range or Continuity setting on your meter. You should see less than 1Ω resistance. More that that indicates a bad connection between the cluster wiring and the alternator D plug. If the resistance is good, then you have a problem with the connection from the cluster and the wiring plug for the cluster.
 
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