Cluster pulled idk what I’m looking at need help!


5 Year Member
Mar 3, 2010
This is not my car but a friends 93 GT he picked up awhile back. So car came with an optima battery and new stock alternator. Guy told him he changed it but had pulled the cluster but something possibly got loose. So the voltage meter will run normal then drop. He replaced the optima battery bc it was no good, but it’s still having the low voltage, the battery light still turns on and then there is this weird beeping or alarming going on. The rpms, mph, and gas don’t work if I remember correctly. Any ideas or insight what it could be and how we can try and fix it??
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I didn't really have an issue with the stink...
SN Certified Technician
Mar 2, 2015
That sounds like an old aftermarket alarm... might be wired wrong cutting power to the cluster.

The battery light is on a different circuit though. That runs from the alternator to the cluster and back out. The green wire ( I believe ) it should be the same color at the cluster harness.

The best way to tackle it is to pull the cluster end check the printed circuit on the back. People always screw them up.


10 Year Member
Oct 28, 2004
I think that Beeping you are hearing is coming from the Airbag Diagnostic Module, its the little blue box in above the Radio behind the Climate Controls.
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StangNet's favorite TOOL
SN Certified Technician
Mar 10, 2000
Dublin GA
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 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.

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.

The following are diagrams courtesy of Tmoss & Stang&2birds

Alternator wiring diagram for 94-95 Mustangs.

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

Dorman - Conduct-Tite 14 Gauge Fusible Link Wire Part No. 85620
Advance auto parts #85620
Pep Boys - SKU #8637594

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

94-95 Mustang wiring diagrams

Complete computer, actuator & sensor wiring diagram for 91-93 Mass Air Mustangs

Complete computer, actuator & sensor wiring diagram for 88-91 Mass Air Mustangs

Ignition switch wiring

Fuel, alternator, A/C and ignition wiring

O2 sensor wiring harness

Vacuum diagram 89-93 Mustangs

HVAC vacuum diagram

TFI module differences & pin out

Fuse box layout

Mustang 5.0 Lights and Radio schematic, by TMoss:

87-92 power window wiring PowerWindowWiring.gif

93 power window wiring

T5 Cutaway showing T5 internal parts

Visual comparison of the Ford Fuel Injectors, picture by TMoss:

Convertible top motor wiring

Engine mounted fuel injector harness

Location of the TPS, IAB, and the 10-pin connectors on a 5.0, picture by TMoss:

Starter circuit\21328

Alternator diagram for 94-95 Mustangs.
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5 Year Member
Mar 3, 2010
So my buddy pulled the cluster out and here is what we got. Again the voltage meter is on and off. When he put the new battery in the voltage meter went up as normal then awhile later it fluctuated and back down how it was reading in the video. Not sure if he tried figuring out the beeping which might be the airbag diagnostic thinga mahchig like @Shakerhood posted but he is working there. Anyways the rpm, mph and gas needles do not work and these were the pics he sent me today.


I didn't really have an issue with the stink...
SN Certified Technician
Mar 2, 2015
That thing is definitely rigged with the soldered on piece of wire. Theres also a piece missing to the far left that goes to the slosh module that controls the fuel reading.

That printed circuit is one of the main problems. Tell him to take pics of the connector ends that plug into it.

No one remakes the circuits for 87 and up foxes. Wish someone would make one though. You can use the printed circuit section from a 4 cylinder but have to be very careful removing it. I've been successful with swapping v8 tach and speedometer into a 4 cylinder cluster body on a 87. Not too bad just have to be careful separating the black face from the green plastic behind it. ( that stuff has adhesive behind it and can pull off the black coating ). Some masking tape and a fork will work well to remove the needles gently. The speedometer needle might take a little playing to get it set back at the right speed. I use a tomtom or garmin's GPS, that shows vehicle speed, to get it right.

The alternator trigger wire runs through the printed circuit on the cluster. I've seen people patch them like what's shown. The patch wire should be patched directly to the wire that leads to the connector. Its very difficult to get a piece of wire to pinch correctly in that location.

The green stuff on the copper lines is corrosion...that's why I recommend replacing the whole thing.

1990 to 1993 should be the same whether 4 cylinder or v8 except for the speedometer and the tachometer. They read different...85mph for 4 and 140 for v8...tach is also reads different.
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You have a nice rear end there Dave.
15 Year Member
Nov 29, 1999
Mililani, Hawaii
The beeping is the airbag module. It will beep if the cluster is unplugged, or if the airbag lightbulb is out. If you/he wants to just replace the cluster let me know via pm. I have three clusters that are all in good working condition. Two out of 93 5.0 and one out of a 91 5.0.

Feb 7, 2017
Yeah those two tabs are jacked. If you wanted you could come off the harness and make your own wire from the cluster in those two positions to plug in separately.
Feb 18, 2001
That particular trace is the ground IIRC.

Honestly, i'd grab another v8 90-93 cluster, and swap the speedo over to keep the mileage intact. You can try rigging it, but if you are going to pirate another cluster for another ribbon i'd just swap the entire cluster.
Feb 7, 2017
I agree I wouldn't want to go rigging but I understand some people may need an option B if money is tight. I can't remember what those were either I'd have to look myself. I just remember one was for the anti slosh but can't remember the other.