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Old 09-10-2015, 09:17 AM   #13
VetteVet
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Join Date: Jan 2005
Location: Kalamazoo, Michigan
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Re: 68 C10 Yellow wire from firewall to starter/coil.

Quote:
Originally Posted by chuchito View Post
Vettevet, I have been looking all over for info on this subject. Everyone talks about the wire with the resistor and says to replace with a different wire from the terminal block to connect to HEI but it gets confusing on what to do with the yellow wires that tee off with the resistor wire. Everyone makes it seem that there is a yellow wire directly to the original coil from the terminal block. The fact is that the resistor wire goes from the terminal block to a splice where it then transitions into two yellow wires. At least it does on my 72 GMC Suburban. My suburban has HEI and has not run in a few years since working on the body work. I'm trying to get it running and needed to know where those two yellow wires go. Since reading this post, I now know that one goes to the original coil which is not needed anymore but I was stuck on what to do with the second yellow wire. Whether to connect it to the starter or not. Your explanation makes the most sense of all posts I've read. So you are saying that I don't need to connect neither of the yellow wires; one to the original coil, since it is gone, nor the one to the starter. Is this correct?
Yes this is correct, the color of the wires may vary but their purpose is the same. On the stock trucks with coils there are two sources for ignition.
The wire off the ignition switch (pink) that runs to the firewall block inside the cab, and the wire from the starter terminal that joins it after it comes through the firewall block.

When the wire from the ignition comes through the firewall block it changes to a special resistance wire that drops the ignition switch voltage down from 12 volts to around 8 volts to protect the coil during normal running.

This is enough for a good spark once the engine fires but more is needed for starting. This is where the wire from the starter comes in.

When the solenoid engages it acts as a relay to connect the large starter cable voltage directly from the battery, to the other wire in the circuit. This sends a full 12 volts to the ignition coil, to provide a hotter spark during cranking.Once the starter disengages, it breaks the circuit and the ignition current reverts back to the resistance wire from the firewall block.

In the original harness the resistance wire was a cloth covered wire colored orange/white/ and purple.


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When GM went to the HEI ignition they needed a full 12 volts to the coil anytime the ignition was on. They simply removed the resistor wire from the circuit and ran the ignition straight to the HEI coil distributor, eliminating the wire from the starter.


Quote:
Originally Posted by toolboxchev View Post
So I to still have that silly resistor wire running to the starter with a keyed Hei designated wire in it.

No you can disconnect the resistor wire and the starter wires and remove them or tape them off, but then you have to run a new wire from a keyed on 12 volts source directly to the BAT terminal on the distributor.

For a clean look you can remove the cloth covered wire from the firewall block on the engine side and replace it with a 12 gauge red or pink wire and run it to the HEI distributor. You'll have to acquire a new terminal for the firewall block call a Packard 56 terminal I believe.

Or you can do what most of us lazy guys do and just run the new wire from the IGN UNFUSED terminal on the fuse panel through the firewall to the BAT terminal on the distributor.


I should remove that resistor wire? I have had a few electrical problems.
Yes I know and we are here to help with those.



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