I have a 1996 Toyota Tacoma 2.7L 4x4 Extra cab with 297000 miles. When the weather is damp, the horn will get stuck on when I start the truck....my neighbors love it! So, I pulled the fuse for the horn. Am I going to have to replace the ignition if I want the horn to work? Any advice?
Thanks so much!
Don't go tearing into the ignition switch, it has nothing to do with that.
These days either the PCM, or the BCM, or something like a Multiplex controls relays.
So a newer Tacoma has a horn relay controlled like this.
Start at the bottom right and follow the Ground circuit.
See how the Ground circuit goes from the horn button through the Multiplex and energizes the low amperage horn relay's coil by providing a Ground to the coil which makes the horn beep? I highlighted it in purple.
Your's doesn't do that.
Your relay is much simpler. It's a 3 pin relay. No Multiplex involved.
It looks like this.
What's important here is your horn beeps when you turn the key.
So look at the circuit. I highlighted in Red the power to the relay. I highlighted in Purple the Ground to the relay.
It's a 3 pin relay. See how the Control side of the relay (coil) and the Load side of the relay (horn) share the same power input? (again) I highlighted it in Red.
So what does this tell you?
It tells you (because your horn beeps) that the power to both sides of the relay and coming out to the horns is good.
(NOT an ignition switch issue).
So why does the horn beep without pressing the horn as soon as you turn the ignition ON?
2 possible reasons.
1) the relay has failed and it's stuck in the Closed position.
2) Like the moderator said, there's a wiring issue on the Ground Side. (short)
If there is a short to ground it's probably in the steering wheel horn switch. Broken wire "grounding out".
So how do you nail this down?
You have to locate your horn relay and with that 1996 it's not going to be easy. I don't think you'll find any fuse box maps showing that horn relay.
I think they stuck it on a seperate pigtailed relay socket behind the interior fuse box.
So your mission, if you choose to accept it, is to locate the horn relay socket and test if,
1) the relay has failed or
2) if any of the 3 female spade connectors are Grounded (using a test light) when the horn isn't being "pressed" (they shouldn't be)
lol. And it's not mission impossible. 🙂
Not necessarily. You could just have a chafed wire somewhere.
Yep. If he tests the relay socket he'll discover if that's happening by a ground being provided to the relay socket when the horn isn't being pressed
.
I said a short to ground is "probably in the steering wheel horn switch"
.
But you're right and I didn't mean to say that I was dismissing any short to ground between the horn switch and the relay.
.
I'm just saying IF this isn't a failed relay, AND IF this is a short to ground, I'd suspect it in the steering wheel's horn switch wiring at the steering wheel
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I'm certainly not arguing with your position that any wiring chafing (grounding out ) between the steering wheel horn switch and the relay should be investigated first
.
I'm just playing the odds
@jack62
"not necessarily" was my response to PaulBand's suggestion the problem might be in the ignition.
Your analysis is brilliant as usual. Using proper diagrams is the best way to quickly pinpoint electrical problems.
I don't always have access to those, so I have to give generic "most likely" advice.