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I finally got around to upgrading my factory points ignition in my 73 torino 351w. The Accel electronic distributor I picked needs full 12 volts instead of the 7-8 volts the points require. So I got out the factory shop manual wiring diagram and went to town.
You have to remove the cluster, we need to access the ignition switch on top of the column.



Once you get the cluster out of the way, unplug the harness on top of the ignition switch, and look for the red w/ light green stripe wire.



We are going to replace this R/LG wire. It has a built in resistor that terminates at the harness firewall junction behind the fuse panel. you will need to access the junction block closest to the fender on the inside of the car. however you need to unbolt them from the outside.



Here is a picture of the 1973 wiring diagram. It shows the bypass wire joining at the spade terminal of the R/LG wire. You need to join it with your new wire, otherwise your car will not fire while cranking.



Pull out the female spade terminal, and replace it with a new one that includes the bypass wire and your new wire. I used a red 14 gauge wire to run from this plug to my ignition switch.



Re-assemble everything, be careful mating up the firewall plugs as the terminals can bend easily.



You should now have 12 volts at your + terminal on your coil while engine running.


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I called msd about this when I upgraded the Galaxie from points and was told to leave the resistor wire in place. I called back again because it just didn't sound right and was told the same by another person. I thought all CD units needed 12v to function correctly but its been 8 years now without issues but I am remove it anyway. Nice write up by the way.
 

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Discussion Starter #3
i found out i needed to change because the coil didnt seem to get the energy it needed at high rpms running at resisted volts. once i changed to full 12v no more breaking up at 6 grand plus.
 

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My MSD got better also after switching from that resistor wire, But I think the underdrive pulleys were playing a part in it too,,, switched wires and put in a 130 amp alternator,,its like a new car!!
 

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One of those things I have been wondering since seening this is with the resistor wire. I understand it was for the points, but why would the duraspark ignitions have it as well?
Do they not get a full 12v?
Why was the voltage dropped down?
 

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Discussion Starter #8
i dont know if the early 74 duraspark ignitions ran the resistor setup. i dont think the later ones did. I personally have never added a duraspark setup, only removed them. there are cleaner and better ignition choices now.
 

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I went to check the volts at the + side of the coil and it read -.096 What am I doing wrong? I still have the stock wiring setup.
 

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Discussion Starter #10
with the engine running, put the positive lead on the + side of the coil, and negative lead to ground. it should read either 7-8 or 11-12 volts. ( make sure your range is correct on the meter) if its the lower reading you have a resistor wire.
 

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I'm not understanding something. Do I need to 'replace' the R/LG wire from the ignition switch to the junction block or 'add another' 14 gage wire along with the R/LG wire? Please excuse my ignorance as I do not understand automotive wiring. I do however want to have my car working properly.
 

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Replace the resistor wire from the switch to the block but then as previously stated, include the bypass wire so the coil gets full 12volts while in the 'crank ' position.

I did the same procedure on my 69 but left the old resistor wire in the harness and ran a new red one from the switch forward.
Hope this helps....John
 

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Why would this matter with an MSD setup?

The coil gets its power from the MSD, and the MSD gets its power right from the battery. (The large gauge + and - wires)
The small positive wire from the original coil + is just the trigger wire to turn the MSD box on.

If you're just running a hot coil and a factory style ignition that still uses the factory coil + wire to feed the coil, then I can see this being a good idea. Or like the OP with this wire feeding a RTR(ready to run) hot dizzy.
 

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unrelated but you look like a wiring guy.
I have a 351 Boss, dual point.
I checked the total timing on it and wow was about 60+
So I unhooked the vacuum and set the total about 32 and initial is about 12
So all good. Took it for a drive and car feels like a dog won't pull hard.
Factory carb seems ok. But will not let the horses out.
I have had this problem before even with stock ford electronic, was 60 plus too
Everybody should be checking total timing not setting it at idle. I cant imagine how many motors ford wrecked with their crap ignition.
I am tempted to put MSD in but want to keep it stock, but if it wreckes the motor!!!!!
Good info on Torino - if anybody has 72 sport FB for sale let me know (4speed be a dream)
 

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Whoa there son. I just installed a Pertronix I in a 67 FE Fairlane and it states 6 volts will run it but 12volts is better. Makes sence to me.
 

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i have a 73 stang grande with 351 c fmx tranny and factory tach trying to wire like yours.where is the blade terminal is it on the block or the ignition switch my harness that plugs into block has pin connectors any help would be appeciated
 

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Ok, I'm having issues with a MSD install, maybe to do with this resistor wire too. Specifically no charging from the alternator. Mine is a 1973 Mustang,302. Did the MSD upgrade with new coil. Do I need to do anything with the old +,- coil wires to complete the charging circuit? I have no status at the gauge or output from the alternator. All the illustrations I've seen show a 4 wire hook up to the voltage regulator, mine has only 3, why would that be? Thanks, Ernie
 

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Yep.. I have to agree with the person who installed one in the 427. My instructions stated the same so I installed the 12v power relay. WAAAAYYY easier than bypassing resistor wire.
 
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