New wiring harness difficulty

[Fjordlander]

Hello friends,
I have a 76 Scottsdale K10 that I bought from someone locally and have been trying to fix up. I have no experience working on vehicles so I'm learning as I go. My latest endeavor was simply to install a horn (because there wasn't one) but when I climbed under the dash, there were no horn wires to be found. On top of that, the few wires that are there are spliced to pieces and I can't make heads or tails of what the wires are.
So I'm thinking it might be beneficial for me to start fresh with a complete new harness so future projects will be easier. My question is, how difficult will this be for someone with my lack of experience? I have a lot of tools and I'm generally good at fixing things but this is something I've never attempted.

 

[Matt69olds]

Make sure the brake lights and interior lights work. The horn is on one of those circuits. Make sure you don’t have a blown fuse.

First, test the horns under the hood behind the grill. The horns ground thru the mounting brackets. Apply power to the terminal on the horn, it should sound. Sometimes giving them a light tap will get them going if the have been unused for a long time.

Horns good? Plug everything back in and move on to the next step.

Find the black wire in the turn signal switch connector. I believe it’s pin G, that’s the ground trigger for the horn relay. Use a jumper wire, ground the black wire. The horn should sound. If so, the problem is in the column If not, listen carefully for the horn relay to click. No click? Move on.

Find the horn relay. It is a small square box taped to the dash harness about the fuse box. It will have an orange, green and black wire. Disconnect the relay. Use a test light to check for power on the orange wire. If you have power, jumper the orange to green, the horn should sound. If not, you have an issue on the green wire somewhere between the horn relay and the horn themselves.

 

[PrairieDrifter]

I wouldn't take on a wiring harness as a novice. Too many little things to break or mess up. It would take forever and you'd have a lot of questions. All it takes is one wire to be hooked up wrong and it light on fire or melts a harness together, then you're in a world of trouble.

 

[fast 99]

There are several harnesses on these trucks. Under hood, chassis, under dash, ect. If you can isolate which harness has been altered and just deal with that part it might be do able. Commonly under dash harness is mostly where the problems are. If a used harness close to the same year with similar options can be located, it would be just a matter of plug and play. However, at some point you will have to be able to read a wiring diagram. An aftermarket harness isn't something I would recommend. They are generic in nature and require extensive systems knowledge. Even a inoperative horn can be caused by other issues besides wiring.

 

[SquareRoot]

If this is too personal, please forgive me. How old are you and what's your background?

 

[SquareRoot]

There are several harnesses on these trucks. Under hood, chassis, under dash, ect. If you can isolate which harness has been altered and just deal with that part it might be do able. Commonly under dash harness is mostly where the problems are. If a used harness close to the same year with similar options can be located, it would be just a matter of plug and play. However, at some point you will have to be able to read a wiring diagram. An aftermarket harness isn't something I would recommend. They are generic in nature and require extensive systems knowledge. Even a inoperative horn can be caused by other issues besides wiring.

True story. In high school I owned a 67 Chevelle. Everytime I honked the horn it killed the engine. Never figured it out before I totaled the car but that's another story.

 

[Fjordlander]

If this is too personal, please forgive me. How old are you and what's your background?

I'm 29. No background in automotive but I've always fixed things around the house. Obviously not the same but I enjoy fixing things and I'm trying to learn automotive now

 

[Fjordlander]

Make sure the brake lights and interior lights work. The horn is on one of those circuits. Make sure you don’t have a blown fuse.

First, test the horns under the hood behind the grill. The horns ground thru the mounting brackets. Apply power to the terminal on the horn, it should sound. Sometimes giving them a light tap will get them going if the have been unused for a long time.

Horns hood? Plug everything back in and move on to the next step.

Find the black wire in the turn signal switch connector. I believe it’s pin G, that’s the ground trigger for the horn relay. Use a jumper wire, ground the black wire. The horn should sound. If so, the problem is in the column If not, listen carefully for the horn relay to click. No click? Move on.

Find the horn relay. It is a small square box taped to the dash harness about the fuse box. It will have an orange, green and black wire. Disconnect the relay. Use a test light to check for power on the orange wire. If you have power, jumper the orange to green, the horn should sound. If not, you have an issue on the green wire somewhere between the horn relay and the horn themselves.

The lights all work however there are no horns in the car. One of the POs removed them and never put in replacements and the wiring that should be there according to a diagram I found is nowhere to be found.
I did find the horn relay but it doesn't do much without the horns.

 

[Fjordlander]

I wouldn't take on a wiring harness as a novice. Too many little things to break or mess up. It would take forever and you'd have a lot of questions. All it takes is one wire to be hooked up wrong and it light on fire or melts a harness together, then you're in a world of trouble.

This is all I needed to hear lol. Thank you.

 

[Fjordlander]

There are several harnesses on these trucks. Under hood, chassis, under dash, ect. If you can isolate which harness has been altered and just deal with that part it might be do able. Commonly under dash harness is mostly where the problems are. If a used harness close to the same year with similar options can be located, it would be just a matter of plug and play. However, at some point you will have to be able to read a wiring diagram. An aftermarket harness isn't something I would recommend. They are generic in nature and require extensive systems knowledge. Even a inoperative horn can be caused by other issues besides wiring.

I'll look into finding an under dash harness. That certainly sounds easier

 

[SquareRoot]

I'm 29. No background in automotive but I've always fixed things around the house. Obviously not the same but I enjoy fixing things and I'm trying to learn automotive now

Ok cool. Your teachable. We can walk you thru it. Might be time consuming and frustrating at times but we can do it

 

[Fjordlander]

Ok cool. Your teachable. We can walk you thru it. Might be time consuming and frustrating at times but we can do it

Thank you! I will keep that in mind. I'm going to dig around a bit more and see if I can make sense of the wires I've got but when I do decide to tackle the harness I will definitely be on here seeking advice

 

[fast 99]

Don't replace under dash harness unless needed. I just tossed that out from previous experience.

 

[75gmck25]

I agree with fast 99. Don’t replace the entire under dash harness unless it’s really needed. Those wire are usually in good shape (compared to underhood wiring), but have been butchered during a radio installation or an attempt to fix a dash gauge. It’s ironic to me how many times “it’s too complicated” to troubleshoot, but a quick choice to replace the entire harness.

If you have the patience to replace an entire harness, you can also use the OEM wiring diagram to troubleshoot a few cut up wires.

Verify that all grounds are present and properly tightened down is the first step. Then start tracing power wires that activate “things”. The only exception is the interior lights, which have constant power, and turn on by switching the grounds (door switches or headlight switch).

 

[Snoots]

Get a multi-meter, voltmeter, DMM; whatever. NOT a test light.