2004 Horn Wire

Discussion in 'Gen 2 Prius Main Forum' started by picassopigeon, Nov 17, 2021.

  1. picassopigeon

    picassopigeon Junior Member

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    My horn is no longer working. It started off where I'd lost just one of the two horns up front, but now there is nothing.
    I can hear the relay clicking in the fuse box area when the horn is pressed, and the fuse is all ok.
    I've now installed new horns and they also don't work, so I guess there must be an issue with the cable from relay to horns.
    How can I gain access to the under side of the fuse box to rewire the horns on a whole new cable? Or is there an easier way of replacing this cable?
    Thanks
     
  2. ChapmanF

    ChapmanF Senior Member

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    Getting into that fuse box is quite a chore, and there might be some diagnostic opportunities you haven't exhausted yet to locate just where the fault might be. Do you have access to a multimeter?
     
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  3. picassopigeon

    picassopigeon Junior Member

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    Thanks for the reply, yes I have access to a multimeter.
    I'd dearly love my horn back as it's a MOT test failure. That's due at the end of January, so I've a little while to get it going again.


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  4. Tombukt2

    Tombukt2 Active Member

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    Are your horn wires showing voltage when the horn button is depressed

    SM-A715F ?
     
  5. picassopigeon

    picassopigeon Junior Member

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    I've got voltage through the fuse, but nothing at the horns.
    As I say I can hear the relay clicking when the horn is pressed, so I'm thinking the wire between the relay and the horns must be broken somewhere.

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  6. ChapmanF

    ChapmanF Senior Member

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    If you find the fault anywhere outside of that fuse box itself, you've got much less of a chore on your hands.
     
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  7. mr_guy_mann

    mr_guy_mann Senior Member

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    Another possibilty is that the contacts of the relay itself are bad. This is assuming that the horns actually work- been bitten by that. Maybe try swapping a relay for another one (that has the same part number). My next step would be getting a wiring diagram and testing at the relay socket. I would check to see if the terminal and wire that goes to the horns is open or intact.

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    #7 mr_guy_mann, Nov 18, 2021
    Last edited: Nov 18, 2021
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  8. Tombukt2

    Tombukt2 Active Member

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    Yeah I'd be looking right on the other side of that relay before it gets out of the box too far to be deep in the wiring in the front end of the car I bet it's right there at that relay by the looks of things in these Priuses they take on moisture and water like Mom watering a plant it's unbelievable

    SM-A715F ?
     
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  9. pasadena_commut

    pasadena_commut Active Member

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    Me too. Definitely test that the horns actually work before doing anything else. Unplug and put 12 volts across each. If they don't work, give them a hard tap a couple of times. I had a horn which "stuck" but worked fine again (for many years) after that treatment.

    Then look carefully at the connectors on the horns and whatever plugs into them. If anything looks at all dirty clean it up with some contact cleaner. If there is corrosion which won't come off on either side replace either the horn or its plug.

    The instructions here may be helpful:

    Replacing Horns on 06 Prius | PriusChat

    If after all of that, and after you replace the relay with a known good one, and it still doesn't work, then you may want to borrow or buy a tool like this:

    https://www.testequipmentdepot.com/klein-tools/datacomm-testers/tone-probe-testers/tone-probe-test-trace-kit-vdv500-705.htm

    to trace the path from one or both ends: relay output (with relay not present) and horn input. If you are lucky the break might be some place that you could reach easily. However, it could also be buried deep in a cable bundle which is only accessible after much disassembly in the engine compartment. Still worth looking, though, as the failed horn might indicate rodent damage, and you could have other wires gnawed through at the same spot that you just don't know about yet.

    If there is a break and it isn't any place convenient, just run new wires directly from the relay output to the horns over any convenient path. I would be tempted to get a couple of horn connectors cut off a harness in a junkyard and splice onto those, leaving the originals hanging. Then if it is ever convenient to fix the broken wire(s) in their currently inaccessible location while some other work is being done, you can remove the new wires, and put it all back the way it was supposed to be.
     
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  10. Tombukt2

    Tombukt2 Active Member

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    Some plate type horns have a set screw you loosen nut after smacking on metal table to loosen vibe plates . Apply voltage and adjust that but to proper amp pull or make it sound correct tighten lock nut. Or replace Fiamm work well

    SM-A715F ?
     
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