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90 Mustang GT voltage/wiring troubles?

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90 Mustang GT voltage/wiring troubles?

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Old 10-06-2008, 09:35 PM
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ButkusJr
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Default 90 Mustang GT voltage/wiring troubles?

So here we go...
I have tired myself for the past 3+ days trying to figure out the problem. First, let me start off by saying that I just recently (last week) tore my whole dash apart and did all that happy stuff evolving a new heater core, so if that info helps...here we go.

My car died just recently and I thought I just exhausted the battery on the car trying to fix and tune some stereo and miscellaneous parts on the car. I figured it would be a good investment to by a good battery, so I did. After the new battery installation, I ran the car for a while to see if everything was ok. It wasn't, my battery gage was around 12 volts and testing the battery with a volt-meter, it was running at about 11.5, and the gage wouldn’t really move at all when running the car. I thought it was a bad connection with the wires behind the instrument panel. I tore the IP apart again and checked the connection, which was good. So then I thought it was my alternator. I took my old one off and inspected it, and it caught when it was spun freely in a small spot. I thought what the hell, I should get a good alternator for the car too, so I bought a new one (which I kind-of regret now cause the old one tested fine). Hooked the new one up and still the same results as before. So then I went and tested all the connections on the alternator, battery, coil, and found nothing out of the ordinary. I also tested all the battery cables, wires to and from battery and alternator. I replaced the pigtail coming off the alternator thinking corrosion was the cause of the bad voltage, and still, the same results.
I am running out of ideas...and help would be greatly appreciated!!
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Old 10-06-2008, 11:01 PM
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Your alternator should be putting back around 14vt to the battery when the car is running. What is is putting back? I had a similar issue and it was an in-line fuse. Get a light meter and check out your wires.
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Old 10-07-2008, 10:59 AM
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everything that i test on the system is what the battery reads...11.5 give or take a bout .1
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Old 10-07-2008, 01:26 PM
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1. If voltmeter reading indicates 2 volts or over battery voltage (over voltage), proceed as follows:

1. Stop engine and place ignition switch in the ``On'' position, then connect voltmeter negative lead to the alternator rear housing.
2. Connect voltmeter positive lead first to the alternator output connection at the starter solenoid, then to the regulator ``A'' screw head, Fig. 10.
3. If the voltage difference between the two locations is greater than .5 volts, repair the ``A'' wiring circuit to eliminate the high resistance condition indicated by the excessive voltage drop.
4. If over voltage condition still exists, check for loose regulator to alternator grounding screws. Torque regulator grounding screws to 15-26 inch lbs.
5. If over voltage condition still exists, connect voltmeter negative lead to the alternator rear housing.
6. Place ignition switch in the ``Off'' position, then connect voltmeter positive lead first to the regulator ``A'' screw head and then to the regulator ``F'' screw head, Fig. 10.
7. Different voltage readings at the two screw heads in step 1f indicates a defective regulator, grounded brush lead or grounded rotor coil. Repair or replace as required.
8. If battery voltage is obtained at both screw heads in step 1f, replace regulator.

2. If voltmeter does not indicate more than .5 volts over battery voltage, proceed as follows:

1. Disconnect wiring plug from regulator, then connect an ohmmeter between regulator ``A'' and ``F'' terminal screws, Fig. 10. Meter should indicate more than 2.4 ohms.
2. If meter indicates less than 2.4 ohms in step 2a, check integral alternator/regulator unit for a defective regulator, then check the alternator for a shorted rotor or field circuit. Perform Charging System Test procedure after servicing alternator. Do not replace the regulator until a shorted rotor coil or field circuit has been serviced.
3. If meter indicates greater than 2.4 ohms in step 2a, reconnect regulator wiring plug. Connect voltmeter ground lead to the alternator rear housing and voltmeter positive lead to the regulator ``A'' terminal screw.
4. Meter should read battery voltage. If battery voltage is not present, repair ``A'' wiring circuit, then perform Charging Circuit Test procedure. If battery voltage is present, connect the voltmeter ground lead to the alternator rear housing.
5. Place ignition switch in the ``Off'' position, then connect voltmeter positive lead to the regulator ``F'' terminal screw. Meter should indicate battery voltage.
6. If voltage is not present, check integral alternator/regulator unit for an open field circuit. Repair as required, then perform Charging Circuit Test procedure. If voltmeter indicates battery voltage, connect voltmeter negative ground lead to alternator rear housing.
7. Turn ignition switch to the ``On'' position and connect voltmeter positive probe lead to the regulator ``F'' terminal screw. Voltmeter should indicate 1.5 volts or less.
8. If more than 1.5 volts is present, proceed to ``I Circuit Test.'' If ``I Circuit'' is satisfactory, replace the regulator and perform Charging Circuit Test procedure. If 1.5 volts or less is present, disconnect alternator wiring plug and connect suitable jumper wires between the alternator B(+) terminal and mating wiring connector terminals.
9. Perform Charging System Test procedure, but connect voltmeter positive terminal to one of the B(+) jumper wire terminals.
10. If voltage rises more than .5 volts above battery voltage, check alternator and starter relay wiring, then repeat Charging System Test procedure, measuring voltage at battery cable clamps.
11. If voltage does not rise more than .5 volts above battery voltage, connect jumper wire from alternator rear housing to the regulator ``F'' terminal.
12. Repeat Charging System Tests procedure with voltmeter positive lead connected to one of the jumper wire terminals.
13. If voltage rises more than .5 volts, replace regulator. If voltage does not rise more than .5 volts, service the alternator.

Last edited by PRO50SC; 11-15-2008 at 02:18 AM.
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Old 10-12-2008, 06:58 PM
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what wires are part of each circut?
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Old 10-22-2008, 10:08 PM
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ok...i replaced both battery cables and checked the one from the starter to the relay...all good and yes...it helped....to a point...

the car sits around 13.5ish if not a little higher/lower.....starts, and dips like it should when it cranks...

when its running though, it creeps up reeeeally slow, and once it gets back to about 13.6ish voltage, that is where it sits.

granted i know that is OK...but i dont like it bein OK. I would like to fix the charging problem so i know it is reliable.

tested the new altenator and it is fine as well (brand new battery too)
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Old 10-24-2008, 09:25 AM
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are there any grounds/wires under the dash that would stop the charging system from working properly?
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Old 11-04-2008, 05:49 PM
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the car drains after a couple days of sitting too
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Old 11-04-2008, 06:10 PM
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Originally Posted by ButkusJr View Post
ok...i replaced both battery cables and checked the one from the starter to the relay...all good and yes...it helped....to a point...

the car sits around 13.5ish if not a little higher/lower.....starts, and dips like it should when it cranks...

when its running though, it creeps up reeeeally slow, and once it gets back to about 13.6ish voltage, that is where it sits.

granted i know that is OK...but i dont like it bein OK. I would like to fix the charging problem so i know it is reliable.

tested the new altenator and it is fine as well (brand new battery too)
I don't see the problem.


As far as it draining the battery after a couple of days, you have a draw somewhere in the system. You'll have to locate that draw.
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Old 11-05-2008, 07:14 AM
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when the flashers are on my battery gage goes up and down with every click of the lights if that helps at all...i've tried pullin fuses to locate the draw and it didnt help

...and it never did it before the heater core transplant...it would run in the 14's-15's

Last edited by ButkusJr; 11-05-2008 at 07:23 AM.
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