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very weird spark problem, '84 mustang


blue83ranger

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This is going to sound very strange, at least to me, i'm in the process of getting my '84 mustang back on the road again for antique plates (in a few months) and one problem it has is the spark. First, it has a 302 w/duraspark and orginally was a 5 speed now has an AOD (may go back to a 5 speed) and has most options you could get. anyway the problem is, you turn the key on, there is power to the coil but when you try to start the motor (motor turning over) the coil looses power. So, the 1 year i did drive the car i had to hot wire it to start it (that got me some interesting looks from people) I already tried a new ignition switch and it had no affect on it. I did notice on the plug for that switch there is a yellow wire that is about 4 inches long (looks like it was cut) and i can't find any info on where it is supposed to go. I looked on about 8 fox mustangs, 2 cougars, 1 thunderbird and every 1st gen ranger i've ever owned and none have this wire. All the other cars i looked in had that spot open. (no wire at all). If i leave this wire going no where (the cut end) it will not start even while hot wireing it (i jump two wires on the ignition switch plug) any ideas on this one? I do have a few repair manuals but couldn't find it in them either. It is possible though this wire has nothing to do with my problem, it just may help it out alittle. and something else i found strange is there is only one wire hooked to the battery. (the smaller wires that actually give the car power and they have fusable links in them) most stuff has at least 2, maybe up to about 5.
 


Explorin94

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The wires you are looking for should be a red/light green and a red/yellow color. The red/yellow is a fused (10 amp) charge-start-run, that one should be spliced at the fuse box with the red/light green wire feeding the fuse box and the red/light green goes to the ignition modulator also as a charge-start-run but not fused. Both these wires come from the ignition switch. But just for shits and giggles try a new ignition modual or atleast see if you got power going into the wire in the crank position. Check out foureyedpride.com and go to the mechanical section their is a wiring diagram for your car.
 
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blue83ranger

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i don't remember for sure, but i think i put on a new ignition modual. (it's been 7 years) but we should have one laying around i'll try a different one to make sure. and i'll do some searching for those wires and let you know what i find, or don't find. thanks for the help.
 

blue83ranger

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i didn't get to work on it that much but i did find out that the ignition switch plug doesn't have those color combos on it. here's what i have. Starting closest to the driver on the drivers side is the mysterious yellow wire, up from that is a black wire that says resistor do not cut GR on it and also a bigger black wire w/green dashes on it. then pink/brown, then i couldn't tell for sure it's either a red or pink wire with green or brown stripe, then a small white wire with red dots on it which is the wire i give power to when i hot wire it. then kinda in the center (not on either side) is a purpleish/white. then starting back up toward the driver is Yellow, then yellow, grey/yellow, and finally a smaller black w/ blue dashes on it. I'll try to check things out better, maybe tomorrow.
 

blue83ranger

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ok i found the fuse that has the 2 wires but the fuse was blown, so i changed it and it didn't make any difference. and the fuse panel says that fuse is for the warning lamps, which is wierd because all of them work. So i used a test light on both sides of the fuse (fuse is out of course) and there is power on both sides. one is a little dimmer than the other. I'm not a wiring expert by any means but if i remember correctly, doesn't that mean there's a bad ground somewhere?
 

Explorin94

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ok i found the fuse that has the 2 wires but the fuse was blown, so i changed it and it didn't make any difference. and the fuse panel says that fuse is for the warning lamps, which is wierd because all of them work. So i used a test light on both sides of the fuse (fuse is out of course) and there is power on both sides. one is a little dimmer than the other. I'm not a wiring expert by any means but if i remember correctly, doesn't that mean there's a bad ground somewhere?
Someone has obviously hacked the wiring harness in that car. If you have power on both sides of the fuse block with the fuse out there is someting seriously wrong. There should only be power on one side of the block and when you put the fuse in then it serves power to the other side and the components from there. Something is back feeding into the dead side of the block that is why the light is dim and you need to find it. My suggestion is to put your test light back into the side that is supposed to be dead when the fuse is out and start pulling fuses until the light in the test light goes out. Although it might not go out depending on how bad the harness is FUBARED Sound like you need a wiring diagram for this car. My suggestion is go to Foureyedpride.com then go to the forums and go to the maintenace thread and there are wiring diagrams for the 79-86 mustangs. Youcould even ask the guys there as they are pretty savvy when it come to these cars.
 

blue83ranger

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I found a decent wiring diagram in a repair manual. And it told me how to check the start circuit and with a volt meter it said to check the white wire for the ignition module and that it should have no more than 1 volt less then the bat. when cranking and i had a consistent drop, I stopped when it hit about 9 volts, bat. had a charger on it and was about 14. i'll check that site out. This car is hurting my brain.
 

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