Wiring ID help - firewall

[Snuffy Smith]

I have been digging through old posts on the major Square Body forums and going over wiring diagrams to try to find an answer, so far I have not found exactly what I am looking for. Background on my truck, it is an 86 Scottsdale with a 5.3 LS, TH350 and a 75 front end swap making for some interesting wiring combinations.

I am trying to sort out the wiring for the horns to get the truck to pass safety and on the road; when the front end swap was done, horns were not installed so I am tracing the wiring to find the horn wire. Looking to ID the wiring in the pictures, Im a little cautious about wiring and would appreciate some expert input.

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Fairly certain I have the plus for the trans lockup here. Necessary for a TH350?

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Im having trouble tracking down this relay block on the driver's side of the wiper motor on the wiring diagram I have. From tracing wires, I am pretty sure this is the hot wire for the cigarette lighter, wanted to confirm this. There are a couple pictures below of the wire path.

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The red wire from the relay block runs through the firewall grommet into the cab; unfortunately, the wire was cut inside the cab and not connected to anything, but has enough length to reach the cigarette lighter.

Any insight would make this process a lot easier and would be appreciated.

 

[RustyPile]

What you're calling a "relay block" looks to be an added-on circuit breaker.. A relay must have a MINIMUM of 3 wires/terminals, most have 4.. The reason you don't see it on a diagram is because it's not a factory installation so it's anybody's guess as to what purpose it serves. My guess would be it was used to power a trailer brake controller that's been removed. Trace the wires. If it's not connected, remove it and start over.. The cigarette lighter is normally powered from a fuse (marked as such) in the fuse box, not a circuit breaker.

The horn circuits for the years you mention are basically the same.. The black wire in the steering column is the ground path for the horn relay. Consult the wiring diagram.. Pushing the horn button completes the ground path, the horn relay's winding is charged and pulls in the contacts -- horn blows. Power is fed from the relay to the horn through the black with green trace wire. Power for the relay is provided through the orange wire from the always HOT section of the fuse block. Relay is located in the convenience center. Did you check the fuse..

That's the factory's '81 -- '87 design.. Any changes made to the various systems by POs is anybody's guess...

 

[Matt69olds]

Find the black wire in the turn signal switch connector. Use a jumper wire, ground the black wire and listen for a clicking relay.

Off the top of my head, the only dark green wires I can think of would be right turn (which will be in a separate connector on the firewall connector body) temp sender and horn. The temp sensor wire will be on the engine firewall connector. That leave the connector body for the front end. See if there is a dark green wire that’s unplugged , hopefully that’s the MIA horn wire.

 

[Snuffy Smith]

Makes sense about that add on circuit breaker. It has been throwing me off with the wiring diagrams. I should have added that the horn fuse blows when I push the horn button.

 

[RustyPile]

Makes sense about that add on circuit breaker. It has been throwing me off with the wiring diagrams. I should have added that the horn fuse blows when I push the horn button.

Makes sense about that add on circuit breaker. It has been throwing me off with the wiring diagrams. I should have added that the horn fuse blows when I push the horn button.

Blowing fuses indicate a short in the circuit somewhere. I can tell you this: The short is NOT in the steering column. As I explained previously, the horn wire in the column is the ground path.. If it was shorted, the horn would simply sound off (blow) all the time.. It would not blow a fuse.. There are no set of instructions telling where the short is located. Good troubleshooting techniques and knowledge of how the circuit actually works will guide you to the short.. Instead of burning up boxes of fuses trying to find the short, I've been using a Short Finder for over 50 years to guide me.. Here's a link to that tool, I suggest you get this tool and use it in finding this short.

Short Finder | Tool Aid

Use to locate shorts quickly and inexpensively in 12 volt automotive circuits.Eliminates need to remove upholstery and floor coverings.Operates through metal parts, panels, fiber and plastic materials.Connect leads to post of blown fuse then use induction type needle indicator to pinpoint...

www.toolaid.com

 

[Matt69olds]

Disconnect the battery.

Find the horn relay. There will be an orange wire (power from the horn fuse) green (power from the relay to the horns) and a black (ground trigger for the relay.

Remove the horn relay. With the battery disconnected, check for continuity to ground on the green wire. If if shows continuity, start under the hood tracing the green wire to the horns. Hopefully you find a pinched wire from the front end sheetmetal swap.

 

[RustyPile]

Disconnect the battery.

Find the horn relay. There will be an orange wire (power from the horn fuse) green (power from the relay to the horns) and a black (ground trigger for the relay.

Remove the horn relay. With the battery disconnected, check for continuity to ground on the green wire. If if shows continuity, start under the hood tracing the green wire to the horns. Hopefully you find a pinched wire from the front end sheetmetal swap.

Matt, Unlike earlier square bodies, the horn relay on '86 models plugs into the convenience center like the turn signal flasher.. Much like the fuse box, access to the back of the convenience center is a bit difficult. Some disassembly is required. Not so with the tool I suggested. That's why I suggested the use of it.. The blown fuse is removed and the circuit breaker that's part of the tool in installed in it's place.. The circuit breaker makes and breaks and no harm is done to the harness.. An inductive pick up ammeter is used to find the short. The only difficulty is figuring out how to keep the relay engaged during the "search". A good explanation of exactly how the tool functions is posted on the site.

I hardily agree with your suspecting a pinched wire from the sheet metal swap.

 

[Snuffy Smith]

It looks like I have found my problem, or at least part of the problem. The Black with green tracer wire was cut off at the rad support and grounded behind the headlights. Ugly Truck Experience has a good video on Youtube about wiring the horns through the LS fuse block, I'll be going this route to wire in new horns.

 

[greyghost]

ugly truck experience ..utuber who specializes in LS swaps to SB. from horn wiring to lites using ECU underhood fusebox very detailed n simple, using relays