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Discussion Starter · #1 ·
Another stupid electrical question. My wiring diagram says there is a 20 guage YELLOW wire that goes to the + side of my coil. Well it SHOULD go to the plus side of my coil but since I don't have a stock ignition it appears to be wired to supply my MSD with a switched 12 volt source. I believe it is supposed to run from the "R" lead on the Solenoid to the + on the coil.

Another wire should go from the + on the coil to the firewall junction. That wire ( on my wiring diagram) is labled 20 W / R / B. The 20 WRB seems to be missing in action and likely was deep sixed by the original owner.

So what is my question you ask? Is the yellow wire which goes from the solenoid the coil + (on a stock system) a switched 12 volt source that can energize my MSD box and my MSD distrib. The MSD has a requirement for switched 12 volt juice to both the distrib and the control box.

Thanks for all your help with this.

Oman

PS Was that 20 W/R/B wire a resistor wire for running after the car has been started on a full 12 volt? I know that the car starts on 12 volts but they run on a lower voltage to save the points. The car is a 72 if that matters.
 

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"Is the yellow wire which goes from the solenoid the coil + (on a stock system) a switched 12 volt source that can energize my MSD box and my MSD distrib."

No, what it does is provide a full 12 volts from the solenoid to the points coil only in START mode.

"PS Was that 20 W/R/B wire a resistor wire for running after the car has been started on a full 12 volt? I know that the car starts on 12 volts but they run on a lower voltage to save the points."

That's what it was. Good guess.
 

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If that's the only power wire then something has been done to the wiring. The post on the solenoid only provides power when the starter is engaged.

Peter
 

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Discussion Starter · #4 ·
So I need the Yellow wire to power the MSD (Box and Distrib during starting AND I need another full 12 volt source to run the MSD during "Run time". In effect there needs to be another wire (Full time 12 volt) and "run time 12 volt" source spliced together.

Or I can find a full time (Run and start key position) 12 volt source and dump the yellow wire altogether? If I go to the fuse box and get such a source then I no longer need the yellow witre in the car at all. Are there such 12 volt sources that are on at both start and run? Seems like there are 12 volt sources that are on at "Start" OR at "Run" but not both?
 

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The IGN terminal on the fuseblock is hot in both START and RUN. At least it should be if the ignition switch is good. Same set-up as the 73s did to run HEI. No resistor wire and no yellow wire. Just a constant 12 volts.
 

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Oman, for MSD ignition you need to run dedicated 12volt wiring to the box and to the coil all the time, this is assuming you did it right and replaced the dist. also, if you just added a coil and box to the point system you need to run the run side of the wiring through a ballast, all of which is a waste of time. Put in a good electronic ignition and be done with it.
 

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Discussion Starter · #7 ·
Well well well. It certainly seems that something is not Kosher in the way this thing was installed.

So the plan now is to deep six the yellow wire altogether.....outta the car G-O-N-E GONE! Then I will run a wire from the ign. lug on the fuse box out to power the distrib. and the 6-AL box.

Mystery is where the "run time" electrical supply is coming from. Hmmmmmmm more searching. Ah I love cleaning up someone elses work. If you are not gonna do it right don't do it.

Thanks again guys.

Oman
 

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If it doesn't start until you let go of the key, then look to change out the ignition switch. I''ve told a couple of guys to use the yellow wire when they had this problem but it's only a work-around.
 
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