'80 Cobra Fell Into My Lap. Couple Things Got Me Stumped...

strangebronco

New Member
Apr 6, 2016
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Hello all, new here, new to everything mustang really.

I "accidentally" became a mustang owner just recently, my uncle donated me his 1980 Cobra - he's moving overseas and he says he can't see himself ever getting round to finishing his old project car.

I'm really quite new to all of this (i have a little automotive tech knowledge-not a lot!, will have to figure out the puzzles as I go along ... right now 2 things have me stumped, and keep me from firing up the engine :

1. He installed a lightweight/small-size starter motor and I have no idea how to connect the cables. I include photos here if anyone knows which should go where ...

Note : that is a 1987 Mustang GT engine he dropped in the engine bay, it was originally a 2.3 turbo (carbed) car. He said the 2.3 was slower than a toad, it had to go. So I have a 1980 wiring harness, and a 1987 V8 in there.

and 2. same problem with the alternator ... I don't know how I should hook up the '87 alternator to the '80 wiring harness ... here are some photos of what I think were the 1980 alternator connections (he chopped everything when he yanked the 2.3) ... anyone here can tell me which one needs to be connected to which one ?

Thanks v much !
There are a couple more puzzles headed my way, but for now I'll try to get these fixed.
If/when I fix these, I should at least be able to fire the engine up - for the first time since it was dropped in the Cobra !!

Here's the aftermarket starter motor and its four connections (a,b,c,d) ... where do I hook these up to ?
Two small cables were zip-tied to the Battery cable ... should they go anywhere here ?
Cobra - New Starter connections SS.jpg

Do A, B, C and D and 1,2,3 connect at all ? Or should 1,2,3 all go to that bulky solenoid below here ?


Here's the original starter solenoid ... it has three connections - not sure what needs to go where ... ?
Cobra - New Starter connections S 2 S.jpg

X,Y and Z ... do you line up with anything on the pictures above or below here ???


Here's the alternator of the new, 1987 GT engine ... it also has cut-off cables that want to go somewhere .. but where .. ???
Cobra - 1987 Alternator connections, ALT side S.jpg

Stumped trying to figure out where A, B and C should go.


And I spotted these 3 chopped-off cables on the 1980's wiring harness ... the big cable actually has the same black & orange marks as one of the 1987 alternator cables ... but I don't know what needs to be connected where - and in fact, maybe these 3 cut-off cables don't even go to the ALT, but should go to the starter solenoid ??! Please help !
Cobra - 1987 Alternator connections, CAR side S.jpg

... do A,B and C line up with anything on the previous pics ? Would love to know !

Thanx all
Mike
just outside Moab, UT
 
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Starter solenoid wiring 92-93 Mustang or earlier Mustang with upgraded high torque mini starter.
attachment.php?attachmentid=53216&stc=1&d=1201020653.gif



Here's an alternator test path for use with later model alternators. It has some wiring diagrams that will be useful.


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 15 April 2012 to add simple check for regulator failure in Engine off ignition on, battery fully charged section, item 2.

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.) 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 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. .

attachment.php?attachmentid=64167&stc=1&d=1286329941.gif

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.


attachment.php?attachmentid=64898&stc=1&d=1292685364.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.

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
 
If you decide in the end to really make this thing run, start a progress thread in the general discussion area.

Lots of people with various talents on this forum.

This would be a fun one to watch. Got a feeling you'll be needing a new harness for this, but I'll let the people that know talk about that, I paint cars.

jrichker is our genius without a title saying it. Listen to him. He will post very thorough solutions to what you need to know.

I hope you decide to make this car run.