Engine Bay Wiring Identification

[CJM72]

I'm wiring up my LS Swap in my 72 Blazer and trying to make sense of a lot of loose wiring and connections that were left by the PO. Been studying the wiring diagrams, but I can't seem to match some of these up. Looking to the board for help identifying these!

First up is a group of wires coming out of a firewall grommet on the driver's side just above and to the right of the junction block. I have a large pink wire and a blue/white, brown/white, and black wire coming out.

The large pink wire goes to this plastic connector.

The Blue and Brown wire go to this connector. Another Green wire is also in the connector and I think this might have gone to a temp sensor or something like that.


Next up is a pair of yellow wires and a green wire that come across the gutter from the driver's side over to the passenger. One yellow was hooked p to the HEI that was in it. The other yellow and green wires were just cut.

[CJM72]

I have a couple other loose random wires and vacuum hoses. Here is a connector with a green wire and a short black wire with ring terminal. This exits the firewall on the passenger side near the AC box.

And here is a random vacuum line with a T in it that is just open to atmosphere.


For the record, this in AC truck and I'm assuming some of these wires are related, but all of that stuff was disconnected and missing when I bought it. Also, all of the emissions gear was gone as well. Trying to clean things up and get everything working again.

[CJM72]

Update. The pink wire goes through the fire wall and plugs into an Ignition Unfused slot on the fuse box.

Did the factory use these unfused slots for certain accessories? I can't figure out what the plug with two yellow wires feeds either. They attach via a connector to a black wire that goes to 'Cluster Feed' Plug. Another black wire links that plug up to a silver box on the firewall. Not sure why one of the two yellow wires is just hanging.

Wondering if I'm going to have to pull the whole dash apart to understand where all these random wires go! Already broke a wire that was feeding something from the other 'Unfused Ignition' slot. Could be the late model radio that the PO installed.

[truckster]

I can't help you with all of them, but the first one is left over from the TCS and is unneeded. If you look under the dash you'll probably see that it's connected to something that looks like the heater relay.

Pic #2 is the ignition wire.

Pic #3 is the AC wiring. It connects to the AC clutch.

The vacuum line probably went to the AC blend door.

Here's a link to a wiring diagram that may help you:

http://67-72chevytrucks.com/vboard/s...d.php?t=185856

[CJM72]

Originally Posted by truckster

I can't help you with all of them, but the first one is left over from the TCS and is unneeded. If you look under the dash you'll probably see that it's connected to something that looks like the heater relay.

Pic #2 is the ignition wire.

Pic #3 is the AC wiring. It connects to the AC clutch.

The vacuum line probably went to the AC blend door.

Here's a link to a wiring diagram that may help you:

http://67-72chevytrucks.com/vboard/s...d.php?t=185856

Thanks Truckster. I don't see the TCS system on the wiring diagrams which is part of the problem! The pink ignition wire isn't on the diagrams either that I can see. Was that stock or something that was added when they covered to HEI?

Pic #3 is the other end of the TCS wiring. I'm guessing pic #5 is the AC wiring. Thanks for the help. Now just got to figure out the green and yellow wires related to ignition. I see the yellow wires on the schematic so I'll have to trace them back.

[CJM72]

Update #2: Two yellow wires traced back to combine to the pink wire that goes to the junction block on the firewall. The wiring diagrams say that should be an orange/purple wire. It says resistor wire right on, so I'll have to replace it if want to power my PCM off it. Interesting side note, I could not get the old 350 that was in it running well for the life of me. Tried all sorts of carburetor adjustments, but it would just fall on it's face when you tried to accelerate. Ran well in park, but under load fell apart. I think the last PO was using the resistor wire to power the HEI!

Question is, what was the giant pink wire for? Was that supposed to bypass the resistor wire and go to the HEI?

[CJM72]

The green wire that runs from the junction block with ignition and starter wires is the temperature sender wire. I think I installed an adapter and stock style sensor in one of the heads, so I'll need that wire if I want my gauge to work. Just adding the last bit of info in case anyone reads this in the future.

Wrapped up the AC wire for future use. Capped the loose vacuum line. Cut out all the TCS stuff and removed the large pink wire that must have been for an HEI conversion. Replacing the yellow wire and resistor wire to feed power to my PCM. This actually opened up a grommet I can use to send ally LS cab wires through (gas pedal, OBD, brake switch, check engine light, and Speedo and tach). I had jammed them through the oil pressure line hole but this is much more direct.