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Discussion Starter #1
Hi Guys,
I have a new engine coming for my 66 and had some questions as I am relatively new to swapping engines.
I pulled the old engine last weekend. I have a small bunch of wires coming through the firewall near where the steering column come through and was wondering if anyone knows what they are? I know a couple of them went to sensors on the old engine and I one of them is probably from the ingnition.
What I am looking for is what wires I need to keep and which I dont. I want to rewire the ones that I should keep as once they go through the firewall it is sort of a mess with splices everwhere.
The new engine will have a Holley Sniper if this makes a differance.
Thanks to all who can help me out,
Trevin
 

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I would strongly suggest buying GM shop manual and wiring diagram booklet for your year, since you are new to this. There are two main harnesses that come out of the firewall - the engine feed and the light. There are also sub harnesses for things like the wiper motor.

The light harness is the bigger one and goes along the driver's inner fender. You will want basically everything in there, but will likely need to make modifications. It feeds the lights, alternator, horns, etc.

The engine feed goes to the starter, coil and various motor sensors. The pink coil power wire is a resistive wire, not full 12 volts, good to be aware of that. I have never installed one of these systems, so no idea what in this harness you would retain.

All of these harnesses are reproduced and American made. So if your wiring is totally trashed you may want to start new. Possibly with a wiring upgrade kit like from American Auto Wire.
 

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There is no telling what has been done wiring wise to your car unless you know who did what or did it yourself. If you are going to run a Sniper there will be some wires that will have to go back inside the car to make it work. I really like the handheld screen on the Holley stuff. There will be a temp sensor and oil pressure sender as well for the fuel injection. It will also have a coil lead, a switched 12v lead and probably some other stuff I'm over looking. It will also need to be grounded and have a constant 12 going to the battery. There is a fused wire already in the fuel injection harness for your fuel pump. It really is pretty straight forward. I was a little intimidated the first time I messed with a throttle body injection unit but I've helped on four or five now including my own and I'll probably never buy another carburetor.
 

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Discussion Starter #4
I would strongly suggest buying GM shop manual and wiring diagram booklet for your year, since you are new to this. There are two main harnesses that come out of the firewall - the engine feed and the light. There are also sub harnesses for things like the wiper motor.

The light harness is the bigger one and goes along the driver's inner fender. You will want basically everything in there, but will likely need to make modifications. It feeds the lights, alternator, horns, etc.

The engine feed goes to the starter, coil and various motor sensors. The pink coil power wire is a resistive wire, not full 12 volts, good to be aware of that. I have never installed one of these systems, so no idea what in this harness you would retain.

All of these harnesses are reproduced and American made. So if your wiring is totally trashed you may want to start new. Possibly with a wiring upgrade kit like from American Auto Wire.
Thanks! I will order some books today.
Trevin
 

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Make sure you get the GM books, not the Chilton or similar books that are always floating around. This is the service manual 1966 Chevrolet,Chevelle,Chevy ll,Corvette,Chassis Service Manual | eBay

Then there is a separate wiring diagram. If you want to be comprehensive with your books, there are also the Fisher Body Service Manual and Factory Assembly Manual. You can probably skip the Overhaul Manual, since it sounds like little of your car's drivetrain will be stock.
 

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Discussion Starter #6
Make sure you get the GM books, not the Chilton or similar books that are always floating around. This is the service manual 1966 Chevrolet,Chevelle,Chevy ll,Corvette,Chassis Service Manual | eBay

Then there is a separate wiring diagram. If you want to be comprehensive with your books, there are also the Fisher Body Service Manual and Factory Assembly Manual. You can probably skip the Overhaul Manual, since it sounds like little of your car's drivetrain will be stock.
Thanks SouthBay2s! I will get this one too. Where do you live? South bay?? I am in SJ.
Trevin
 

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I live in Oregon but was born and raised in the Los Angeles south bay area. That is where the name came from. I did coincidentally go to UCSC and then live / work in the silicon valley area for a handful of years. Too expensive and crowded so we left. I have friends and family throughout the PNW into Montana, so it was a logical move.
 

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I live in Oregon but was born and raised in the Los Angeles south bay area. That is where the name came from. I did coincidentally go to UCSC and then live / work in the silicon valley area for a handful of years. Too expensive and crowded so we left. I have friends and family throughout the PNW into Montana, so it was a logical move.
I was born in SJ and been here all my life. I agree Silicon Valley is crazy $$$$. I would like to get out of here but the wife has family here....
 

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The factory under-hood wiring on these cars was originally divided into 2 separate harnesses. One harness is primarily for the front lights & horn but also includes the voltage regulator & alternator wiring. The other harness contains the wiring for the starter & ignition, along with wires for the oil & temp warning light switches.

If you go to the "Best of Electrical" sub-forum, there is a post titled "All Generation Wiring Schematics" where you can find some diagrams for your car.

According to those diagrams, there should be 2 rectangular 8-cavity connectors on the firewall bulkhead. One for the front light / alternator wiring, and the other for the engine wiring. The one for the engine wiring should contain the following wires:

yellow = ignition switched power feed to the windshield wiper motor.
black = switched ground to the wiper motor from the switch.
purple = ignition switched power to the starter solenoid (only live in the "start" position).
multi-colored resistance wire = ignition switched power to the + coil terminal.
dark green = coolant temperature switch (for the "temp" warning light).
dark blue = oil pressure switch (for the "oil" warning light).
and 2 empty cavities on the connector.

You should be able to keep the majority of these wires in the stock configuration, repairing / replacing any damaged wires or connectors as needed. The multi-colored resistance wire that feeds the + coil terminal originally had a cloth-like insulation covering and will also have a solid (as opposed to stranded) core wire. With many electronic ignition systems, the resistance wire can be eliminated and replaced with a standard copper wire.

If there are numerous cut/spliced/damaged wires on the old harness, it might be worth purchasing a new engine harness. I believe they are available in versions that are already modified for electronic (HEI) ignition, where the resistance wire has already been replaced with copper.
 

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Discussion Starter #10
The factory under-hood wiring on these cars was originally divided into 2 separate harnesses. One harness is primarily for the front lights & horn but also includes the voltage regulator & alternator wiring. The other harness contains the wiring for the starter & ignition, along with wires for the oil & temp warning light switches.

If you go to the "Best of Electrical" sub-forum, there is a post titled "All Generation Wiring Schematics" where you can find some diagrams for your car.

According to those diagrams, there should be 2 rectangular 8-cavity connectors on the firewall bulkhead. One for the front light / alternator wiring, and the other for the engine wiring. The one for the engine wiring should contain the following wires:

yellow = ignition switched power feed to the windshield wiper motor.
black = switched ground to the wiper motor from the switch.
purple = ignition switched power to the starter solenoid (only live in the "start" position).
multi-colored resistance wire = ignition switched power to the + coil terminal.
dark green = coolant temperature switch (for the "temp" warning light).
dark blue = oil pressure switch (for the "oil" warning light).
and 2 empty cavities on the connector.

You should be able to keep the majority of these wires in the stock configuration, repairing / replacing any damaged wires or connectors as needed. The multi-colored resistance wire that feeds the + coil terminal originally had a cloth-like insulation covering and will also have a solid (as opposed to stranded) core wire. With many electronic ignition systems, the resistance wire can be eliminated and replaced with a standard copper wire.

If there are numerous cut/spliced/damaged wires on the old harness, it might be worth purchasing a new engine harness. I believe they are available in versions that are already modified for electronic (HEI) ignition, where the resistance wire has already been replaced with copper.
THANKS RAY! I am going to go over the wires this weekend. This information helps a LOT!!!
Trevin
 

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I have some pdf files of the wiring for 66-67 novas which engine did your car originally have?
 

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i have a 66 an needed a wiring schematic. i found a very nice one at classic car wiring.com. its 18'' x 12'' an sealed in clear plastic. all the wires are color coded an very easy to follow. has wiring for 4-6-8 cyl engines. i needed the schematic to wire in a neutral/back up switch on a 66 auto floor shifter. i'm color blind so my wife had to read all the colors to help me out. i'd say the cost was 20-25 bucks, money well spent.
 
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