92 Charging Problems. Help!

IH8BOWTIES · Mar 23, 2009

I drove my 92 5.0 down to Ennis, TX from Tulsa this weekend for Pinks All Out (not a participant, just spectator) I had been having some charging problems before this weekend. I replaced the neg battery cable and all was well. I had no problems on the way down there. Stayed at my in-laws in Mexia, TX just down I-45. From Mexia to Ennis (about 40 miles) I notices my battery light on and the volt meter drop to about 10 volts just like it did before I replaced the neg battery cable. Revved the engine a little and it came back. Then it would go out again. I finally noticed that this happened when I hit a bump. Now I know that I have something loose. I enjoy the day at pinks. On the way home, it was doing the same thing. Pulled over to see if I could find something loose. No luck. I get to Mexia and start tracing everything. Presto! Loose nut on the solenoid. It started charging again and it charged fine all the way back to Tulsa. I got 27.2 mpg too! Not relevant but impressive. I went to Wal-mart this morning to get some new headlight bulbs for it and on the way back, the battery light comes on again and down to 10 volts. Everything is tight and now I'm dazed and confused. The alternator has been tested and it passed three times. I'm getting voltage to the stator. Could I possible have a blown fuse link? Any help would be appreciated.

93 LX · Mar 23, 2009

have the alternator tested..

87WhiteStang1 · Mar 23, 2009

take a look at your ignition switch.. theres a wire on there that goes to the regulator and if its burnt up or anything it won't tell the alternator when to turn on

IH8BOWTIES · Mar 23, 2009

I'll have a look. Thanks.........

jrichker · Mar 23, 2009

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.

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

Alternator troubleshooting for 86-95 5.0 Mustangs:
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

Diagram courtesy of Tmoss & Stang&2birds

See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host) for help on 88-95 wiring Mustang FAQ - Engine Information Everyone should bookmark this site.

Ignition switch wiring
http://www.veryuseful.com/mustang/tech/engine/images/IgnitionSwitchWiring.gif

Fuel, alternator, A/C and ignition wiring
http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif

Complete computer, actuator & sensor wiring diagram for 88-91 Mass Air Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/88-91_5.0_EEC_Wiring_Diagram.gif

Vacuum diagram 89-93 Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/mustangFoxFordVacuumDiagram.jpg

HVAC vacuum diagram
http://www.veryuseful.com/mustang/tech/engine/images/Mustang_AC_heat_vacuum_controls.gif

TFI module differences & pinout
http://www.veryuseful.com/mustang/tech/engine/images/TFI_5.0_comparison.gif

Fuse box layout
http://www.veryuseful.com/mustang/tech/engine/images/MustangFuseBox.gif

IH8BOWTIES · Mar 23, 2009

Thanks jrichker. I'll get on this tomorrow after work......

IH8BOWTIES · Mar 24, 2009

Ok. I went through all the steps. I had zero voltage at the green wire per step one. Nobody actually sells a fuse link already set up so I had to get the stuff to make one. Got it all put back together and I get the same result. Either I did it wrong or I have other issues. Just for grins, I did a continuity check from the alt output to the green wire and got quite a bit of resistance. About 18,000 ohms. I expected it to zero out. New set up did the same thing. All the other tests passed although my battery voltage is down to 12.25. What is interesting is all the running the engine has done, it hasn't seemed to discharge that much but it won't charge either. I may just say screw it and get me a 130 amp 3g with all new wiring and be done with it. I've got the 4 guage, connectors and fuse. Just need the alternator. I was just hoping I could get another week or so out of this one. This charging system has been giving me problems since I got the car about 5 years ago. Lights flickering, etc. The kid that had it before me had a monster stereo in it on the stock charging system. I think that's where the problems started.......I had to replace the alternator almost immediately after getting it.

IH8BOWTIES · Mar 24, 2009

Well, it seems I found the gremlin. I had a broken wire from the solenoid to the alternator that excites the stator. It's somewhere in the harness. Ran a new jumper wire of the same guage and color. Thanks for everyones help.......

jrichker · Mar 25, 2009

IH8BOWTIES said:
Well, it seems I found the gremlin. I had a broken wire from the solenoid to the alternator that excites the stator. It's somewhere in the harness. Ran a new jumper wire of the same guage and color. Thanks for everyones help.......

If th wire was yellow/white, see iterm #2 on the Tech Note I posted... You probably have a blown fuse link inside the harness.

IH8BOWTIES · Mar 25, 2009

Yeah, I went back over everything again. I had the battery removed from the car this time though so I opted for continuity test on this particular wire. The schematic by tmoss showed an 18 guage link which I found by the solenoid. Tested on both sides of the link and got nothing so there must be another one in there somewhere. Anyway I set up a new jumper wire with the same fuse link setup instead of digging into the harness. Lights have flickered ever since I've had the car and now they don't. This could explain the two fuel pumps I've gone through as well as they felt this "flickering" effect also. I plan on doing a 3g upgrade this weekend. I'm glad to have solved this problem as I would have gotten the same results with the new alternator.
Anyway, without you're help, I may still be out in the garage scratching my head. You've been blessed with a talent. Thanks for sharing a little of it. I really do appreciate it.

matts90lxhatch · Apr 15, 2009

I'm glad I found this thread because I have the exact same issue with the car I just bought.

It's not charging and I have a new alternator and battery in the car. This morning I found a wire burnt into coming from the harness going to the solenoid.

Is a 20 amp blade type inline fuse fine to wire in that spot?

jrichker · Apr 15, 2009

matts90lxhatch said:
I'm glad I found this thread because I have the exact same issue with the car I just bought.

It's not charging and I have a new alternator and battery in the car. This morning I found a wire burnt into coming from the harness going to the solenoid.

Is a 20 amp blade type inline fuse fine to wire in that spot?

What color is the wire? Knowning the wire color would tell me the circuit function and wire size.

Most of the alternator control wiring isn't designed to carry 20 amps. Putting too big a fuse could allow an electrical fire if there is a problem in the alternator circuit.

matts90lxhatch · Apr 15, 2009

jrichker said:
What color is the wire? Knowning the wire color would tell me the circuit function and wire size.

Most of the alternator control wiring isn't designed to carry 20 amps. Putting too big a fuse could allow an electrical fire if there is a problem in the alternator circuit.

I'm at work now and I can't remember the color of the wire but I will let you know as soon as I get home from work.

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