My horn doesn't work . . . found what I am fairly certain is the horn wire on both sides of the engine compartment. . . Anybody have any insight into what this relay location should control and/or why my horn isn't working?

You don't mention what year truck you have, but I'm pretty sure it's very different to my '84. I would suggest you begin with finding a copy of the factory service manual. It should show you where the horn relay is normally located. FSMs in pdf format for most years can be found on the internet if you Google around a bit. You won't find them at this forum for legal copyright reasons.


If you're not particular about keeping the wiring original, you can install a generic relay wherever is convenient for you. A generic relay can be had for far less than even junkyard prices on a Toyota direct replacement.


For example:
http://www.goldmine-elec-products.com/prodinfo.asp?number=G20188

 

Yeah, I looked for the FSMs, but the ones for 89 seem to not exist... :|
Most links I have seen are expired by now.

Any advice on how to find them?

 

According to my 95 wiring diagram the wire from the relay to each horn is orange, and the wire from the relay to the horn button is green/red stripe, that helps.

 

Still searching the internet for the FSM. I know how helpful it can be, but am having a lot more trouble finding it than any of my other cars.

I found a relay that COULD have worked at Autozone (across the street from me), but it didn't change anything. I think the internal schematic might not be the right one, so I am still looking...

Said relay: http://www.autozone.com/engine-management/relay-efi/duralast-relay-efi/269464_0_0

 

Found the FSM for a 1993 Pickup on an archived website *cough*.

But even under "Body Electrical"(the section I would think the horn wiring would be), I don't see anything.

I think I need the while Wiring Diagram for the truck as well...

 

Ok, thanks to a very helpful forum user, I have the wiring diagram for the horn.

Unfortunately it raises a few more questions than it solves. I have a screenshot posted at the bottom of this post.

1. Below is a picture of the backside of my horn. There is only one wire, and I connect it to the non-Ground pin. When I have my multimeter connected to the "Ground pin" and the green/red wire in the engine bay (for the horn), I get it to show continuity when the horn is pushed. That's great. But is there supposed to be something going to the ground pin of the horn button? There is no other connector on the steering column, and I read online that it is self-grounding.

2. What is "L-W" supposed to signify, colorwise on the wiring diagram?

 

Hook up the horn just like in the wiring diagram. The non-ground terminal goes to +12V, and the ground terminal goes to the horn switch, which supplies ground when you want the horn to sound.

 

Yup. Tried that over the weekend.
12V went from the battery directly to the + of the horn.
Horn button on the steering wheel was hooked up as shown above (one wire).

Horn did not fire.

I also jumpered the ground of the horn to a bolt used for ground in the cab, and again, horn did not fire.

Horn was tested minutes before on the +/- of the battery, and it fired perfectly.

 

While there's more than one way to skin a cat, in a case like this I favor taking a systematic approach. I would suggest you begin by wiring it according to the diagram. If the horn still doesn't sound, then troubleshoot with your DMM.

Here's the idea. You have already demonstrated that the horn will sound when it gets +12V and ground. If it doesn't sound, then either it's not getting a solid +12V, or it's not getting a solid ground. Or both.

How can you tell which possibility it is? With your DMM.

With the horn wired correctly, and with an assistant at the horn button, press the button and measure the voltage on each horn lug. These voltages should be measured with the DMM read lead, while the DMM black lead is grounded to the battery (-) terminal. While trying to sound the horn.

Do you measure +12V on the non-grounded pin? And less than one volt on the grounded pin? If not, you need to look at the offending part of the circuit.

 

Still not sure what "L-W" means on the wiring diagram.
Looks like it feed the horn power from the fuse.

Also does "W-B" mean "White-Blue/Black/Brown"?

 

Still not sure what "L-W" means on the wiring diagram.
. . .

It's spelled out in tedious detail in the service manual. Guess you missed it.

B = Black W = White
L = Blue BR = Brown
V = Violet SB = Sky Blue
R = Red G = Green
P = Pink LG = Light Green
Y = Yellow GR = Gray
O = Orange

 

Thank you! Will get it all wired up this weekend and start isolating.

And Iam guessing if it says "L-W" that means it's a primarily blue wire with a white stripe running along it?

 

Spliced into a nearby wire for the +12V, and ran a grounding strap from the Ground terminal of the horn to a bolt securing the steering wheel on.

Horn works now!

 

You might want to redline your wiring diagram to indicate which circuit you've spliced into. We think we'll remember these things - after so many hours of agony - but it's amazing how quickly we forget. If there's any question which circuit it is, you might pull fuses one at a time until you get it.


Congratulations on a job well done.

 

Good idea.

+12V spliced from the smaller gauge blue wire with a white stripe and grey dots going into the windshield wiper motor.
No horn relay is used for this circuit. (Still not sure what relay should go in that slot).

From the numerous trips to the junkyard looking at other truck's horns, this seems to be the same color wire that should have been there. But since the PO moved the fuse box under the hood into the cab of the truck, I assume this wire was clipped somewhere.