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Horn not working, sort-of

Discussion in 'XJ Technical Chat' started by SQLGuy, May 5, 2020.

  1. SQLGuy

    SQLGuy Well-Known Member

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    The horn on my 750RJ is stock. According to the wiring diagram, it's a momentary switch in the left control cluster which grounds the pink wire to sound the horns. No electronics, no relay.

    However, what I have going on is this: once the bike is started, the horn won't work. When it's parked after that, the horn won't work. If I remove the headlight (to gain access to the horns, which are in the bucket) the horn won't work. If I ground one of the pink wires with a jumper at one of the horns, the horns will sound, and, after that, the horn will work from the switch, for a while.

    So, I then disconnected the pink terminals from the horns and measured resistance from there to ground. It drops to about .8 Ohms on the meter when the switch is pressed. Great. Except, that when the key is on, it only drops to 500 Ohms or so. Key off - short. Key on - kind of high resistance.

    What is this? There must be something weird going on in that switch cluster. I guess I'll have to pull it apart, again. Anybody dealt with this before?

    Thanks,
    Paul
     
  2. SQLGuy

    SQLGuy Well-Known Member

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    Well, I took the control cluster apart, and it looks like the switch is good. There seems to be a problem with the ground side of things. I can see where a black wire comes back into the headlight bucket and connects to a number of other black wires. If I disconnect the others, I still have ground from the one that goes to the switch... .5 Ohms, until I turn on the key. Then it rises to four or five hundred.
     
  3. Rooster53

    Rooster53 Well-Known Member Premium Member

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    I don't think the higher resistance with the key on is meaningful. It simply means the probes are across a point that is generating a small voltage affecting the reading on the DMM - I think this would occur because of splices, shared grounds, or perhaps poor grounds depending on where you are measuring.

    I was also thinking the left control directly ties the horn ground to the handlebars. If that is the case then you may have an issue with handlebar to frame resistance causing a slight lack in current flow and reducing the current in the horn solenoid enough that the contacts do not break. Seems you could measure the high and low sides of the horn looking for voltage drop to isolate that issue when the horns are not working, or as a start just measure the voltage across the horn when the button is depressed.

    I guess you can ground either horn manually to get them to operate normally for a while?

    And I haven't really looked but perhaps there is an age factor going on here in that it takes just a bit more current because of binding components within the horn, and knowing the XJ electrical system is weak to begin with this could be a factor also.
     
  4. SQLGuy

    SQLGuy Well-Known Member

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    Nothing should be, though. Ground is ground, and with a fraction of an Ohm to ground with key off, it should take a significant current source to make that read 500 Ohms with key on.

    The horn button does not ground to the handlebars. It grounds to the black wire that runs back into the bucket with the rest of the left side control cluster wiring harness branch.

    Yes, if I ground them manually, they work. No, I don't think age is a factor. I think the ground line from the bucket is the issue. Where is that actually supposed to go to chassis?
     
  5. SQLGuy

    SQLGuy Well-Known Member

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    I noticed the other day that the sidestand relay was only pulling B/W down to a couple of hundred Ohms when the safety circuit was engaged. I bet that's related, too. It uses the same black ground line.
     
  6. Rooster53

    Rooster53 Well-Known Member Premium Member

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    The wiring harness electrical ground is at the ignition coil mounting hardware with two eyelet terminals on the 750 Seca. This gets the ground to the frame. The battery ground is connected to the engine, and engine to frame grounding is through the mounting of the engine to the frame. The 750 Seca did not use an extra ground wire as some did to tie the engine to the frame.

    I just checked an extra left control and what happens is the turn signal ground (eyelet) terminal that ties to chassis in the left control is common with the low side of the horn switch, which indicates they are spliced together in the left control harness. Therefore, since the turn signal ground wire ties to chassis, the horn button will ground through the handlebars as well as return through the black wire.

    I remember being there once, and attributed it to a poor ground or splice as I mentioned above. I would suspect if you disconnected the tail light or other active circuits the reading would be more appropriate - not proven on my end though.
     
  7. Rooster53

    Rooster53 Well-Known Member Premium Member

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    I believe DMM's measuring resistance on the lower scales operate by utilizing a constant current source and measuring the voltage. To produce an error of 500 ohms would only take about 45 mV, which is pretty small when considering poor connections and common grounds through splices.
     
  8. SQLGuy

    SQLGuy Well-Known Member

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    There is no place in the left side control cluster on mine where anything is connected to the handlebars. The horn switch has its own pink and black wires soldered to it, and those go into the harness that runs up along the handlebars. I'll post a photo. Sounds like there may be variations in different years or runs.
     
  9. SQLGuy

    SQLGuy Well-Known Member

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    Unless you are saying that the primary ground for the horn switch should be back through that eyelet and to the handlebars... In which case, I would say they did a questionable job of designing that, but I can reinforce it.
     

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  10. Rooster53

    Rooster53 Well-Known Member Premium Member

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    That eyelet terminal in the picture is grounded when secured with the screw, and that wire is spliced with the black wire on the horn. The whole assembly is then electrically connected to the handlebars when mounted, although you could make a case that it doesn't have to be since it has a separate wire for ground. That said, it might be just a bit better ground to make things work.
     
  11. SQLGuy

    SQLGuy Well-Known Member

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    I'll experiment with that a bit. Thanks.
     
  12. SQLGuy

    SQLGuy Well-Known Member

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    Only got a few minutes to work on this today, but, to cut to the chase, I think the main problem is that I'm reading 500 Ohms from the handlebars to the engine block with the key on. So, any assumption that the handlebars are grounded would seem to be incorrect. I wouldn't be that surprised that grounding through grease covered bearings might be an issue. I think I'm going to add a proper ground wire from the handlebars back to the chassis and see how things do.
     
  13. Rooster53

    Rooster53 Well-Known Member Premium Member

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    Just as a comparison same bike XJ750 Seca 1982:

    At horn pink to engine fin .8 ohms when horn button depressed
    At horn pink to engine fin with key on 471 ohms when horn button depressed

    Handlebar to engine .8 ohms
    Handlebar to engine 120 ohms key on

    Head bearings are upgraded to tapered bearing
     
  14. XJ550H

    XJ550H Well-Known Member Premium Member

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    ground wire from control runs down in sub harness to main harness connector there should be a mating ground wire there.
    if not just add one and use a ring terminal to the ignition coil

    550s do not have the mating wire in main harness and fully ground through the bars. you can get the parts to add one from chacal to make it look good and dissemble easier

    added coment for benifit of 550 owners
     
  15. SQLGuy

    SQLGuy Well-Known Member

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    Interesting. Thanks Rooster. So that high resistance with key on is normal... but still weird to me.

    I put everything back together after cleaning things and tightening the horn terminals, and the horn's been working, but I have to open the cluster once more because the left side actuator for the self-cancelling unit isn't making contact...
     
  16. Reed whitehead

    Reed whitehead Member Premium Member

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  17. SQLGuy

    SQLGuy Well-Known Member

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    Not sure what the point was of Reed's quote that post with no additional info... but, I also thought I had updated this thread after this. Went on a long ride later, and the horn stopped working again. I then pulled the tank and messed with the modular connectors there, and was able to get it to behave or misbehave where the pink wire was connected though one of those plugs. I cleaned, tightened, and applied dielectric grease to all of these plugs, and the horn has been OK since.... but I have not yet done any more long rides. Will maybe take one tomorrow.
     

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