How much of this can I cut off since the AC doesn’t work and I am going to get a new harness when I replace/overhaul the unit… I’m installing a sniper and making sure all my wiring is good before a short breaks the ECU

The guy before me loved electrical tape and upon removing it I see this mess of copper…

 

I am seeing a fire in your future. In addition to the missing wiring, the biggest concern is the melted insulation. What caused it to get so hot? I would throw it all away. Sooner or later you will have to.

 

I agree with above!
If you really want to make sure your wiring is good before sniper install, get a new Starter Extension Harness for your late 77 W/AC...
The 4 wire plug is the F/M side of the starter extension harness that is C403...
I have 2 photos here...
1. Is your posted photo, I numbered the connector cells and labeled them 1-4 (Blue Stars On My Photo Below) plus the High Speed Blower Relay 2 wire plug connector...
2. 3 separate pages showing Connectors Left & Center photos you will find C403 and right photo you will find C136 C=Connector...
The 4th wire on the C403 connector is just a chassis ground or Circuit 150...

 

okay so can I remove everything associated. What’s the limit to the circuit? Can I just get rid of all of the wires going to and from the AC and continue until everything is gone forward of the firewall (AC wires). Adding a picture of the wires forward of the firewall. And something that looks important connected to it.

All the wires fwd of the firewall connected.

I can’t see that very well but is it important… the wires lead to it. To be clear not the ignition leads

 

thank you for all the information. I am under the assumption that the last owner didn’t care to be safe with their electrical work. I have been slowly going through and fixing a lot of the connectors. Something to add is that I don’t particularly care for AC so I’m more looking to remove the wires all together. I bought a PCM with the kit so if I want to fix up the AC I will probably just route it through that. I posted 2 more images to show where I am getting stuck at. Seems like there are also an assortment of colored wires which I believe are from the AC selector switch assembly. A few wires go down to a component under the engine that I’m trying to figure out what it is and if I can cut wires to it.

 

I would suggest you get a schematic for your specific year car. The starter extension harness is notorious for melting, fraying and all kinds of issues. And there is a lot of current going thru it. Replace that as BMTJOE says. Once you replace that harness you can start to follow the wiring in your schematic and see what wires you may need or not need. Wether you have A/C or not you should have the blower wired up. For the DEFROSTER maybe?

You may or may not have much electrical experience, especially with these old cars. If you blindly cut wires, you may loose something important and not realize it. Like a fusible link? Those would be the 3 funny feeling wires down there. When I was a youngster ( a very long time ago) I got my first vette, a 67 vert. I wanted to clean things up so I just went crazy with a wire cutter, not having any idea what I was doing. I came across this white thing on the firewall. It had 2 wires going to it. Maybe I will just cut the wires, remove that thing, and splice the wires back together. Easy peasy. So that is what I did. When I got all done everything looked great, but the car would not start. After what seemed like forever ( remember I had just gotten my first vette , I was 19 yrs old, and girls were waiting for me) I started reviewing what I had done. Back then there was no internet nor were there large laminated wiring diagrams in color. I managed to get a copy of the wiring for that car and I had thrown out something called a ballast resister. Had never heard of one before but it must be important so I put it back in. ( lesson #2, don't throw anything away). The car fired right up and away I went. Lesson learned. The point is you can cause more problems for yourself if you start cutting things down there by the engine that you can't see but might be important. Best case you burn up the new ECU. Worst case is you burn up the car and maybe the garage it's parked in.

Sorry for the lecture but you really don't want to just mess around especially with this harness. Good luck to you.

 

The Red/White stripe wire at C403 is the main power to your headlight switch, protected by a fusible link labeled B on the drawing I provided...
The Purple wire at C403 is your start circuit to the starter solenoid...
The solid Red wire at C403 is your charge circuit, and the main power feed to the ignition switch (BAT3) (BAT2) and the horn circuit.
The Solid Red wire also feeds the High Speed Blower Relays N/O set of contacts. The solid Red wire is protected by fusible link labeled A on the drawing...
Now for Connector C136, the Orange wire energizes the High Speed Blower Relay...The Black wires are common chassis grounds Circuit 150...
Now back to the Orange wire at C136 there are two conditions where this wire comes into play (HOT)
1. When you set your fan speed selector switch to HIGH it energizes the HSBR ...You might want that for Heat/Defrost etc...
2. When you select MAX/AC it also energizes the HSBR...
You tell me...
Do you need Headlights?
Do you need a Starter Circuit?
Do you need a Charge Circuit?
Do you want the heater to blow at high speed?
If all above are needed, purchase a new Starter Extension Harness for your year, install it and move forward with you sniper install...

 

How sure are you about those? I already tracked the entire headlight circuit when I fixed it before. Is the starter the component at the bottom? Also I am thinking of getting a new harness just unsure what the Blue wire with a white stripe that was cut. It connects to the harness

 

I also have a late 77 that I have owned for over 40 years, and I can also read a line diagram.
Yes, the starter is bolted to the engine block. The Blue/White striped wire should land at the hood pin switch...It's part of the factory alarm circuit.

 

okay thank you! I will order the harness when I can afford it. Should be able to next paycheck. Appreciate all the help. Who knows maybe the AC will work when I replace the harness! Also PCM question. There is an AC power breaker on it if I’m not mistaken. Have you had any experience with Sniper or know if it’s worth the hassle moving the power lead to the PCM?

 

Just make sure when you order the starter extension harness you purchase the correct one, there is a difference between early and late 77...
About the PCM, I have no experience with those circuits, but if you can post a link to the install instructions I will find the time to look it over...
Just be careful with those exposed wires.
Personally, I would disconnect battery until you are ready to install new harness. I will help you as much as I can...

 

okay so looking over it again it says ACC. Also I’ve seen early and late 77 is there big difference and how could I tell. A previous comment mentioned Late 77. I haven highlighted all the things that are in the kit. Is there anything else you think I should route through?

Highlighted in pink is what comes in the sniper

These are the dimensions… only place I can see it fitting is by the passenger front wheel well (engine side)

 

I will look over the diagrams you posted.
I will also post a link of the starter extension harness for your late 77...

 

Here is a link to the starter extension harness:
I have used Top Flight Automotive before, there pricing is usually a little lower vs. other vendors vendors...
https://www.topflightautomotive.com/...oning-77-late/
Is this the Sniper diagram you purchased?

 

Yes it is minus the hyperspark. Heard of you mess that up the engine blows up and would rather not take that risk. Thank you for the harness link

 

You asked about the ACC outputs, 9 & 10 are Switched Positive 2amp outputs and would land on #86 of a 5 pin Relay
11 is a Switched Negative output and could be used to ground the relays coil, #85...
You would also want to put a inline fuse before each relay...
Here I just added 2 fans for a visual to the drawing, one at 9 (R1) and one at 10 (R2)...
11 is the switched ground to (R1) & (R2)...
These ACC outputs are just optional, but there there if you need them...
Hope this helps

 

okay so and 2 more things. One, can I use the ignition power lead to the PDM and then put the Ignition side of that same lead to go to the ignition? Then I wouldn’t have to run a power wire to the battery. And two, I got a returnless fuel pump but have seen other options online after. It requires me to drill a hole. Should I get the C3 pump or just drill the tank? I am attaching an image of the pump to this.

This is the config of the pump

Side view, position 1 hole on top

Position 2, better in terms of space and position. Will be extremely hard to install

Position 1, towards the bottom of the tank and less space for pump

Btw thank you so much for you have been a real help in all this. I am an aviation mechanic so I’m used to getting full documentation explaining what and why something is getting done. This seems very wild Wild West.

 

Personally, having a new tank I would spend the extra money and get a fuel pump and sending unit that is a plug & play...
https://www.holley.com/products/fuel...hoCgeAQAvD_BwE

 

Here is how I would wire the PDM...
I would run a correct sized wire to the positive Battery, and along with that at the same time run a correct sized wire to the negative Battery...
You may have more but this circuit is switched in the START & ON positions...
It is Circuit #3 at the distributor coil #12 gauge PINK wire...

I imagine the reason, is you need power in both Start (Cranking of Starter) and ON for the fuel pump...
How good are you at doing a good electirical splice?

 

I use heat shrink and make sure it’s crimped properly. The pump that I have is a plug and play for the Fuel Injector. Not the tank sadly.