What is this wire for?

[Randy and Easton]

Hello y’all,

This picture is of inside the engine compartment looking at fuse box. We are just working on the electrical stuff and wonder what this was used for ? On the very bottom , left cluster. Anyone have a diagram of what wires are on engine compartment side? Most of the printing missing on inside fuse block due to age. Thanks so much

Randy and Easton

 

[Originalthor]

What year of truck is it.

 

[hoagster]

The info you need is in here! drill down to 1976 and look at the firewall schematic! My guess is a ground by the color.

https://www.gmsquarebody.com/threads/1973-1991-wiring-manuals.14498/

 

[Randy and Easton]

1976 C10

 

[Randy and Easton]

I’ll solder a new wire and ground it. Only thing inside that is not working is horn. New wheel and complete column rebuild. Horns work when I ground them through relay manually, but I’m having a heck of a time figuring out how to test the ground contact in steering column without taking it apart again! I hooked up a button to get it inspected last week and. Guy never tested horn! Anyway, not high priority but just somewhat aggravating
..

Randy and E

 

[tobiahr]

The info you need is in here! drill down to 1976 and look at the firewall schematic! My guess is a ground by the color.

https://www.gmsquarebody.com/threads/1973-1991-wiring-manuals.14498/

Do you happen to have the new links for the 81/82 models. The ones in [SIZE=3]hatzie[/SIZE]'s sig no longer work

 

[Turbo4whl]

About the horn, you ground the relay and it works. Okay no trigger from the button. The wire that joins the turn signals wires up the steering column for the horn is black. Did you try back feeding that wire with a probe to ground? The horn should beep same as if you ground the horn button. If you can't get the horn to beep back feeding that black wire, the horn problem is before that.

Then that black wire that isn't hooked to anything at the firewall could be the horn trigger wire broken out of the harness. If the horn button contact is good, (they fail a lot) you could test that wire. Hook a test light or meter to the battery positive, probe that loose wire at the firewall. Push the horn button and if that is the horn trigger wire the test light will light.

Last thought is the horn button contact did fail and a previous owner cut the wire to add a dash button. When selling or trading the truck extra horn button was removed. Very few people try a horn when they buy a vehicle.

 

[Newcman1]

I'm new to this forum and this is my first post. I've read a lot of other posts that have helped me out a lot with my 85 suburban K10 resto-mod so maybe I can try to pay it back, assuming any of this is correct. I looked at the wiring diagrams and it looks like the cut off wire is or should be dark blue at least per the wire diagram. Maybe spraying some rubbing alcohol on the wiring at the block will let you see the colors better and match them up to the wiring diagram.

The diagram of the firewall junction block is actually a mirror image of your pics since the connector is shown as if you're looking into it after it has been unplugged. At the block position labeled 31 there's a wire labeled 20 DK BLU 31. So that's a 20 gage wire and it's part of the #31 circuit. Tracing the wires shows it going to OIL PRESS SW and another OIL PRESS unit. I can't really tell from the symbol exactly how the second OIL PRESS unit operates but it's also tied into the CHOKE HEATER.

The dark blue wire passes through the firewall junction block into the truck and goes to the gage cluster OIL TELL TALE - STOP ENG on the flexible circuit behind the gages. So grounding the cut wire might light up that warning light if it's still good. I think before grounding any unknown wire I'd check it to see if 12 volts shows up on it during any ignition key positions.

The wiring diagram for the horn relay is attached to help with the testing that Turbo4whl proposed. Although I think the horn wire coming from your junction box to the horn is actually a 12 gage dark green wire at least according to how I'm reading the prints. It would probably be the large dark green wire in the middle of your pic.

I hope this is helpful or that more knowledgeable guys on here will point out where I'm wrong.

 

[Rusty Nail]

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[Turbo4whl]

@Newcman1 In your last picture #5 shows the black wire that is the horn relay trip to the horn button. It says horn and shows the horn switch completing the connection to ground. The green wire from the horn relay is the current supply to the horn when the relay is triggered by the horn button.

 

[Randy and Easton]

Thanks guys. All new wheel and electrics in column. Tried hooking test light up to 12V and hit the horn wire coming to steering column connector and no ground shown but black wire that was in the horn relay connector shows no ground either so from the column connector back to horn relay that line is not grounded either. All the new insides were LMC and maybe I need to take column apart and see if the horn grounds at the button. It’s not a big deal, hooked up a makeshift for inspection and it passed so not high on the punch list but sure will drive you to drink sometimes…

Thanks. Randy and Easton

 

[Randy and Easton]

Here is what original horn relay connector looked like when I took relay out. I am not sure but that black cut wire in engine compartment maybe the ground for this relay so I will test it as y’all suggest to see what it may have been…..

 

[Radiohead]

At least he didn't find the self destruct terminal. Never ground out that terminal. It turns your square body into a Ford.

 

[Newcman1]

@Newcman1 In your last picture #5 shows the black wire that is the horn relay trip to the horn button. It says horn and shows the horn switch completing the connection to ground. The green wire from the horn relay is the current supply to the horn when the relay is triggered by the horn button.

Yes that's how I read it too. The dark green 12DG wire from the horn relay then goes through the firewall connector to the horn. It would be better if I had included more of the wiring diagram.

The black wire from the horn relay goes to the DIR SIG SW labelled as 28. I'm not sure if that's "pin" 28 or "circuit" 28. These wiring diagrams can be challenging to figure out.

 

[Randy and Easton]

Update (I know it’s been a year) that black wire on the engine side of the fuse block is constant hot so I’m still trying to figure out where it goes. I just used a test light, not volt meter yet.

More to come. Everything in the truck works, the horn is. It in column but have a dash button at this point for inspection purposes.

Randy and E