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Ignition resistor wire removal 1973 torino

39K views 21 replies 15 participants last post by  PSIG 
#1 · (Edited by Moderator)
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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#2 ·
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.
 
#7 ·
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?
 
#21 ·
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?
the resistor is for the coil if the coil doesn't have an internal resistor you need to drop the voltage or the coil will overheat. the duraspark needs to get 12 volts of it's own
 
#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.
 
#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.
 
#11 ·
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.
 
#12 ·
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
 
#13 · (Edited)
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.
 
#14 ·
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)
 
#19 ·
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
 
#22 ·
It depends on the version of DuraSpark. Many comments assume only one type, but here are 3 families of DuraSpark, and all of them must have full 12 volts to the module. The relay mod or bypass is good for this task.

2 of the 3 types (green, blue and some others) must have a resistor to the coil, as the module does not handle coil dwell to limit amps.

The 3rd type (DS-I red grommet) controls dwell and uses a low-ohm coil with no resistor for high energy (HEI power), and uses full 12V to both the module and the coil. With the much higher amps, only the relay mod should be used for DS-I (red).

Hope that helps with the differences, and comments must refer to the grommet color or type when posting, in order to avoid mistakes.

From Ford references. DS-II connections shown. DS-I has one wire position swapped:
 
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