Helo...can anyone tell me what is making my headlights go out when the main beam is on...the sidelights and headlights work fine until the main beam is switched on and then the headlights go out..they come back on if i turn the main beam off..the car has just failed the mot because of it. 1998 fiat punto.
Many thanks for any replies
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nt
If the sidelights stay on, then two blown main-beam filaments is the likeliest cause. Commoner than you'd think.
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Im confused ...maybe i didnt word my question right in the first place..
turn sidelights on- sidelights work fine
turn headlights (dipped beam) on-headlights work fine
turn main beam on-main beam works .. but headlghts (dipped beam)go out
they are separate bulbs for dipped and main beam
my brother told me that not all cars keep headlights (dipped beam)on when main beam is on but i presume headlights and main beam are supposed to work together on my car because it failed mot
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nt
Nearly all dip beams go out when main beams come on. Yes; there are a few that don't - but no main beam fails the MOT either way.
Have you checked the main beam bulbs?
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Sounds like i have no problem then because the main beam works fine..
it failed because offside headlamp not working on main beam...main beam works but dipped beam does not when the main beam is on...dipped works fine when and main beam is fine...they just dont work together so i changed the blown headlamp bulb on way home from mot
failure sheet also lists (although this is in brackets on the form) headlamps going out on main beam..... but they still do with the new bulb fitted so im thinking the mot tester doesnt know what hes doing...he did seem to be much stricter than the older bloke that usually does it and i have been busy and missed the free re-test so i may take it somewere else to mot it
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nt
I'm easily confused - but I can't make head-nor-tail of that. There was a blown bulb on one side only? Is that what the fail was for?
As far as I recall - too pushed elsewhere to check the tester's manual - if both dip and main work when commanded, then that passes. They don't need to be on together.
Having dip on with main isn't always a good idea - too much light in front of the car.
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It's quite usual for dipped beam to switch off when main beam is selected - it's just that you don't normally see it because both lamp filaments illuminate the same light unit.
In fact, it's not unknown for people to bodge around with the wiring to make the dip filament stay on while the main filament is on - when these two filaments are housed within the same glass envleope, overheating soon follows, and the life of the bulb is short.
If I have interpreted the OP's question correctly, I think he is being over-zealous. It may be worth prompting the tester, and ask him to look up the correct wording for the "reason for rejection"
Number_Cruncher
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i assume you must have the gt headlights with the extra main beam lights integrated into the standard size headlight,its a fiat so it is totally possible that the way you describe is possible,but more likely something is wrong,take the back cover off the lights and see if all the wires are factory untouched
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