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Poking through the wiring diagram and wiring harness for my '74, I've come up with several questions.

Background info: I'm removing the Gen 1 engine and tranny, and substituting in an LS2 / 4L60E, so questions are pertinent to what I should keep, what I should remove, and what can be used in a different way. I'm pretty good with AC (housing) electricity, but I have little knowledge of DC.

Once I get all this figured out, I may try to post an entire guide to the underhood wiring, pictures and all.

1) The "idle stop solenoid" seems like it's only useful for a carburetor. Can I ditch that wire all the way back to the firewall?

2) Related to first question: The feed wire for the idle stop solenoid looks like it's just an ignition-on power feed. Is this true? If so, could it be useful for something in my engine swap or other future accessory?

3) Kind of related to first question: There is another wire on the same feed as the idle stop solenoid that goes to the positive side of the coil, and then makes its merry way over to the starter. What does this translate to in the LSx world? Is this also just an ignition-on power feed? Should it go to the positive on all the LS2 coils, and to the starter? If it goes to the starter, which pole?

4) What are the three wires on the Gen 1 starter? They are A) black/red - this one is obvious - it's the feed from the battery and the positive supply to the rest of the system, B) purple - looks like a power feed to the rest of the electrical system. If so, why? You would think you would feed power directly from the red wire coming off the starter. Why two power feeds?, and C) yellow. Why do you need three wires?

5) There is a dark blue wire that goes to something called a "pressure switch". What does the pressure switch do?

6) There is a "temperature switch" that feeds into the firewall. Is this just an on/off wire for the idiot light? Does this switch (or wire) have any life in the LSx world?
 

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2,188 Posts
Poking through the wiring diagram and wiring harness for my '74, I've come up with several questions.

Background info: I'm removing the Gen 1 engine and tranny, and substituting in an LS2 / 4L60E, so questions are pertinent to what I should keep, what I should remove, and what can be used in a different way. I'm pretty good with AC (housing) electricity, but I have little knowledge of DC.

Once I get all this figured out, I may try to post an entire guide to the underhood wiring, pictures and all.

1) The "idle stop solenoid" seems like it's only useful for a carburetor. Can I ditch that wire all the way back to the firewall?
Not needed

2) Related to first question: The feed wire for the idle stop solenoid looks like it's just an ignition-on power feed. Is this true? If so, could it be useful for something in my engine swap or other future accessory?
Not needed
3) Kind of related to first question: There is another wire on the same feed as the idle stop solenoid that goes to the positive side of the coil, and then makes its merry way over to the starter. What does this translate to in the LSx world? Is this also just an ignition-on power feed? Should it go to the positive on all the LS2 coils, and to the starter? If it goes to the starter, which pole?
Not needed
4) What are the three wires on the Gen 1 starter? They are A) black/red - this one is obvious - it's the feed from the battery and the positive supply to the rest of the system, B) purple - looks like a power feed to the rest of the electrical system. If so, why? You would think you would feed power directly from the red wire coming off the starter. Why two power feeds?, and C) yellow. Why do you need three wires?
Need A,B starter wire from start position C not needed
5) There is a dark blue wire that goes to something called a "pressure switch". What does the pressure switch do?
Not needed
6) There is a "temperature switch" that feeds into the firewall. Is this just an on/off wire for the idiot light? Does this switch (or wire) have any life in the LSx world?
Not needed
 

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1974 Nova, 1977 Nova
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2,056 Posts
Poking through the wiring diagram and wiring harness for my '74, I've come up with several questions.

Background info: I'm removing the Gen 1 engine and tranny, and substituting in an LS2 / 4L60E, so questions are pertinent to what I should keep, what I should remove, and what can be used in a different way. I'm pretty good with AC (housing) electricity, but I have little knowledge of DC.

Once I get all this figured out, I may try to post an entire guide to the underhood wiring, pictures and all.

1) The "idle stop solenoid" seems like it's only useful for a carburetor. Can I ditch that wire all the way back to the firewall?

2) Related to first question: The feed wire for the idle stop solenoid looks like it's just an ignition-on power feed. Is this true? If so, could it be useful for something in my engine swap or other future accessory?
Yes, the idle stop solenoid is only useful for a carb.

It's an "accessory-on" rather than "ignition-on" feed though. Meaning that it's only powered when the ignition switch is in the "run" or "accessory" positions. Unlike an "ignition-on" feed that's powered in the "run" and "start" positions. Still might be useful for something though.

3) Kind of related to first question: There is another wire on the same feed as the idle stop solenoid that goes to the positive side of the coil, and then makes its merry way over to the starter. What does this translate to in the LSx world? Is this also just an ignition-on power feed? Should it go to the positive on all the LS2 coils, and to the starter? If it goes to the starter, which pole?
It sounds like you're describing the ignition/coil feed wire but it shouldn't be on the same circuit as the idle stop solenoid. It's a special resistance wire that reduces the voltage to keep from burning up the points. And the wire leading down to the starter is a bypass that feeds full voltage to the coil for a hotter spark while cranking. All of this would be totally useless for the LS engine. But you can remove that resistance wire at the bulkhead connector and utilize that slot as an ignition feed. Pretty much the same thing that's done when converting from points to HEI. Completely remove the bypass wire going to the starter.

4) What are the three wires on the Gen 1 starter? They are A) black/red - this one is obvious - it's the feed from the battery and the positive supply to the rest of the system, B) purple - looks like a power feed to the rest of the electrical system. If so, why? You would think you would feed power directly from the red wire coming off the starter. Why two power feeds?, and C) yellow. Why do you need three wires?
(A) Yes, this is a battery positive feed to the rest of the system. Should be protected by a fusible link.
(B) The purple wire is used to engage the starter. It eventually leads back to the ignition switch but goes through a neutral safety (auto trans) or clutch safety (manual trans) switch on the way. And on 74 it's also run through the seatbelt-starter interlock relay.
(C) The yellow wire is the ignition resistor bypass that I described above. Only useful with a points ignition system.

5) There is a dark blue wire that goes to something called a "pressure switch". What does the pressure switch do?
That would be the oil pressure switch that activates the "OIL" light on the dash. Even when using an oil pressure gauge, I like to keep the stock oil light hooked up as a quick attention getter. That's easily done by screwing a Tee fitting into the engine's oil pressure port and connecting the gauge to one leg of the Tee and the pressure switch into the other.

6) There is a "temperature switch" that feeds into the firewall. Is this just an on/off wire for the idiot light? Does this switch (or wire) have any life in the LSx world?
Yes, that's for the "TEMP" light. As with the oil light, I like to keep these hooked up even with a temp gauge. A Tee isn't very practical for this so I usually leave the temp switch in the stock location and plum the temp gauge to the intake. With an LS engine swap you should be able to do something similar as long as the engine has more than one temp sender location available.
 
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