Light Shorting out

Discussion in 'Motorhome Chat' started by gazzeroo, Feb 15, 2015.

  1. gazzeroo

    gazzeroo Funster

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    Has anyone had this problem or know of a solution? My bathroom light blew the 10amp fuse recently, when I turned it on. I thought it might be the light itself so I got a new one and installed it, but it was only on a few seconds and blew the fuse again. I have taken it out again, taped up the exposed wires and all the other lights work ok. Could it be that one of the wires has chaffed somewhere and exposed the inner core thus shorting out? I cannot easily get to the wiring as it is behind the bathroom panel. Any suggestions would be most welcome
    kind regards
    gary
     
  2. treetops1

    treetops1 Funster

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    Hopefully no mice lol.Check for water under the bath 10 amp fuse seems a bit big for a light ,not that that would would be the problem .don't forget to turn off at the mains if your messing with the wires under the bath.lol.
     
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  3. Jonkil

    Jonkil Funster

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    You state you have taped the exposed wires and all the other lights work OK?
    If you leave the bathroom light on, even with the missing light will the fuse blow after a few seconds? .... If I'd does then the problem is in the wiring leading to the light, if it does not blow then the problem is obviously in the light unit. Put a H7 bulb in situ, if it lights and works ok then your light fitting is obviously the issue.
     
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  4. Jaws

    Jaws Funster Life Member

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    Beat me to it Jonkil !!
     
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  5. Wickolad

    Wickolad Funster

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    May also be worth checking wiring behind the switch that terminals and wiring secure.
    The lighting in the bathroom should be 12v only in MH.
    With switch in off position, use a test meter to check between resistance between the +ve and -ve of the feed to the light fitting. It should be open circuit, if there is a low resistance reading, then there is a short on the feed.
     
  6. gazzeroo

    gazzeroo Funster

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    Thanks for all that, just to explain further! The light is fixed to the bulit in corner shower unit. The light has an integral switch so I have removed the whole unit. There is now just a red and white wire coming thru the hole in the plastic. These are now taped up and secured to the cubicle and all the other lights work ok. I replaced the light with a brand new one and it still blew the fuse. I am sure it must be the wiring but am confused as to what would make it faulty. It is all 12v on the lighting, I have replaced the fuse like for like and the information on the cover of the fuse box says 10amp so I am certain that is correct. We were parked up when the fuse blew, all I did was turn it on, previous to that it worked fine. The new light is a 12v led, but I wouldn`t have thought that would be a problem. Again any advise much appreciated
    gary
     
  7. Jonkil

    Jonkil Funster

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    Gary, is the switch part of the new light fitting?
    What we're trying to establish/rule out is where the "short" is.
    We will assume for now the switch is separate from the light fitting, remove the light fitting, tape up the wires, SWITCH THE SWITCH ON..... See if the fuse blows now ?.... Are the other lights working?
    If the fuse still blows then a problem exists somewhere else but NOT the light fitting.
    If the fuse remains intact the problem IS in the light fitting.

    Your problem is that the circuit is demanding more than the fuse can deliver, actually a draw of over 120 watts (12volts x 10amps) which is considerable, the only scenario this really can happen is there is a short in the circuit somewhere, either in the light fitting or the switch/cable run.

    Have you hooked the new LED up with correct polarity? LED's are polarity dependant i.e... + & - need to be connected to the correct terminals.

    Hope this helps.
     
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  8. Daifuse

    Daifuse

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    Gary, when you say 'a new light' , do you mean a new bulb or a new complete fitting? If you've replaced the old fitting with a new one are you sure that perhaps the mounting screws or part of the fixings aren't touching something in the wall that could be shorting out the +ve to the chassis or something else? If you're just replacing the bulb in the old fitting then the fault is obviously in the fitting if all works OK with the wires taped up. (incidentally, 'bulbs grow, lamps glow) - it helps to get terminology correct!)
     
  9. Wickolad

    Wickolad Funster

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    Just in order to clarify things in my mind, the light fitting you have completely removed contains an integral switch. Therefore the 2x wires you have taped up are the 12v +ve & -ve. If the fuse does not blow now, the fault is within the light fitting, as I would presume the fuse protects the whole of the habitation 12v lights.
    If the above is all correct as I understand it to be then using a test meter set for continuity if it has that feature with audible buzzer. If not set it to Ohms, Omega sign on the tester. Remove the lamp from the fitting.
    With the unit in the off position, put probes of test meter into the +ve -ve connectors of the fitting. If using continuity feature with buzzer it should remain silent. Switch the fitting on, the tester should remain silent if it sounds, there is a short circuit in the fitting. If the test meter is set to Ohms, then the reading should be infinity as there should be nothing there to make a circuit. If there is a reading, then something is shorted so you then need to open up the fitting and check all wires for chaffing against each other or metal frame.
    Hopefully you should be able to identify the problem. (y) Are you able to take a picture of the fitting at upload it so as to give an idea what circuitry is involved? May then be able to assist further. Lance.
     
  10. Jonkil

    Jonkil Funster

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    Excellent,
    We "dilbert" minds think alike !
     
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  11. Wickolad

    Wickolad Funster

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    Thats brilliant haha, well done finding that. (y)(y)
     
  12. bertiebasset

    bertiebasset Funster

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    Forgive me for jumping in here but if the switch only has 2 wires going through it, it is either switching pos + or neg - and the light fitting is connecting the opposite.
     
  13. Jonkil

    Jonkil Funster

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    Correct,
    So it the fuse blows when no light fitting is in situ then the problem lies elsewhere other than the fitting... of course that's assuming the +ve is switched. The -ve should be irreverent unless the +&- are shorting before the switch/light fitting.
     
  14. bertiebasset

    bertiebasset Funster

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    Jonkil,, I agree,, one way to try, as the OP seems to have stated the fuse remains ok and the rest of the lights work ok it the lamp is removed,, would disconnect the lampholder and see if there is a short across the contacts. if so then there is the problem, if not then the fault lies after the lampholder. IMHO
     
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  15. gazzeroo

    gazzeroo Funster

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    Thank you very very much for all your replies, you really are a very helpfull lot. I will try all of the suggestions at the weekend and will let you know how I get on. Just to reiterate, the old and new lamp both have integral switches, both blow the fuse when connected, but all the others lights are ok when the bathroom light it not connected. The only thing I am not sure about is if I got the polarity right when I connected the new led light, would this blow the fuse if I got it wrong?
     
  16. Jonkil

    Jonkil Funster

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    The new light is LED you state. If the new light has a circuit internally then there may be a protection diode to prevent reverse polarity and if so then yes it is designed to protect the circuit and may well blow the fuse
     
  17. gus-lopez

    gus-lopez Funster

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    I thought with most Led's that if connected the wrong way around they just did not work ?
     
  18. gazzeroo

    gazzeroo Funster

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    Thanks Jonkil, I think I`ll check that first.
     
  19. Borderland

    Borderland Funster

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    A protection diode to prevent reverse polarity will normally stop any current flow if connected wrong way so not likely to blow fuse.
     
  20. Jonkil

    Jonkil Funster

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    When a protection diode blows it will cause a short across the input +ve and -ve terminals.
     
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