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5.0L (1979-1995) Mustang Technical discussions on 5.0 Liter Mustangs within. This does not include the 5.0 from the 2011 Mustang GT. That information is in the 2005-1011 section.

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Old 11-09-2005, 04:35 AM   #1
sgt_pepper17
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Default '84 GT wiring question

I have an 84 GT. I recently put a rebuilt motor into it and ran into some ignition problems. The wires were so messed up that I got fed up and tore out the electronic ignition and put a points destributer in with a pertronics igniter to replace the points themselves. It worked great; however, I have a question about one of the wiring harnesses. There is one on the driver's side by the electronic ignition box. It has about 6 wires coming out of it and is rectangular. It was hooked up but none of the wires went anywhere when I bought the car. I pulled the harness apart and left it open. What does this do? What's the point of this harness? Also, I've noticed that the car no longer charges. May this have something to do with that harness? I hooked up the old alternator just like it came out, however I decided to run V belts on this car. Would the charging problem be in relation to this or the harness or something else all together?

Erik
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Old 11-09-2005, 09:26 PM   #2
tinman
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Default RE: '84 GT wiring question

Take a pic of the engine bay and post it on here. I think you may have
Fu---d up the regulator. Can't tell from my wiring diagram here...........
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Old 11-10-2005, 01:25 AM   #3
sgt_pepper17
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Default RE: '84 GT wiring question

I don't have a digital camera. The key-on line (green/ red stripe) shows no power what so ever when the key is on. The return line shows a constant 12 volts and the field is working. I've been lookin at the wiring diagrams and it shows a red/green striped line going to the EEC. What is the EEC. That's where my 12 volts is supposed to be coming from.


Erik
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Old 11-10-2005, 04:00 PM   #4
sgt_pepper17
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Default RE: '84 GT wiring question

bump
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Old 11-11-2005, 12:42 AM   #5
tinman
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Default RE: '84 GT wiring question

Erik; EEC= Electronic Engine Control. I think it's supposed to the 'brains' of the whole thing. Not intended to be used with anything except electronic distributor.
Think that NAPA sells them cause it sounds like yours is cooked.
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Old 11-12-2005, 06:24 AM   #6
sgt_pepper17
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Default RE: '84 GT wiring question

Well I have a new Brain Box, but it doesn't matter. I put a points distributor in it and then installed a pertronics ignitor. It works great and starts up fine, but it doesn't recharge. The voltage regulator has 12 volts constant and the 12 volt ignition wire I keep hookin up drops to 10 volts after I hook it up. The field wire shows 4.5 volts when the vehicle is running and the battery shows 12.5 volts while idleing and jumps to over 13 volts when reved up... I don't know what I'm hookin up wrong. Let me know what you think. Thanks.

Erik
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Old 11-12-2005, 01:55 PM   #7
tinman
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Default RE: '84 GT wiring question

First, try checking with another gauge.
If that don't do it, go all the way to the alternator and check everything.
Aren't these things fun?
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Old 11-12-2005, 04:08 PM   #8
sgt_pepper17
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Default RE: '84 GT wiring question

Did that. 12 volts constant, 12 volts ignition, 4.5 volts at the field wire. I'm only getting 12.5 volts back to the battery. If I rev the motor to about 2000rpms then I get 13.7 volts. I'm thinkin it's the voltage regulator. I bought a new one and it works better than the old one but didn't fix the problem.
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Old 11-12-2005, 11:56 PM   #9
sgt_pepper17
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Default RE: '84 GT wiring question

Well I checked and rechecked everything but came up empty handed. I'm begining to wonder about my voltage regulator. If it's not sensing a load from the outside, it's not going to send the appropriate number of volts to the alternator. If that's happening the alternator will not put out the appropriate volts. Is there another sensor that detects load? Also, I've got the key-on wire going to the possitive side of my coil. Is that okay?

Erik
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Old 11-13-2005, 11:34 AM   #10
90GTRagtop
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Default RE: '84 GT wiring question

Sounds like it very well could be the regulator. You could always try to old style alternator test. Fix a wire so that you can briefly apply 12 Volts to the field and check the voltage across the battery. If it goes up to 14 to 16 volts, the alternator is OK and the regulator probably has issues.
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Old 11-13-2005, 11:34 AM
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