How do head lights work...

[Arthurdaily]

Seems a stupid question I know, but I am a little confused by the original BMC manual!

Now from another thread I know I have sealed beam lights - but they appear to have TWO bulbs in... one filament with no glass, and a small seperate bulb - is that what BMC call a 'pilot' light?

So what is supposed to come on when? I am supposing that the small lights below the headlights, ie with the indicators, come on as sidelights, then the small 'pilot' bulbs is supposed to come on as dipped headlights and then the big filament is supposed to come on as main beam - is that correct?

I know now that the whole glass needs changing if a main filament goes... but I am presuming it needs chaning if the pilot bulb goes as well yes?

I'm not stupid by the way... I have NO lights at the moment and am trying to get 'em working

[Alex'n'Ane]

Yes, unfortunately you cant just change one bulb :\ And you are right in thinking that the sidelights are lower down on the car (possibly combined with indicators depending on year, modification etc) Before changing the unit, check that the power is getting there ok, remove the light and check that there is power getting to both the dipped and main beam (I think there should be a 3 pin plug on the back) (I presume you have found the floor mounted switch). It would be very unusual for both to fail simultaneously, and if neither side is working i'd say its almost certainly wiring (unless the car has been sat for years).

[Arthurdaily]

Hi, yes I have found the floor switch - it seems such an odd design to have to throw away the whole light unit (if I have to in the end) because of bulbs! It seems so... 'unmorris'!

So was I right in saying small bulb for dipped and bigger unprotected bulb for main?

Also was I right in saying the pilot light is what we now call a side light?

Finally - since the headlights 'aim' to the left on a standard UK spec car, I'm presuming any ukheadlight will fit either sidewithout making a difference?

[mike.perry]

If you have sealed beam lights with a pilot light then you have light units for an early Mini which had the side lights in the headlights. The Minor has separate side lights so you do not need them.
Sealed beam units were meant to last longer than bulbs

[Alec]

Hello Arthur,

there are (or should be) two filaments inside the sealed beam unit and it has three terminals at the back. (And yes, if either filament goes you need to replace the whole unit) The side light, as Mike says Minis have, is simply a small window in the mirroring and the sidelight bulb was external to the sealed beam.

Alec

[Arthurdaily]

AH! Right, so I have sealed beam with sidelights below - indeed on close examination my lights only have one bulb in them with two filaments, no actual second bulb, but there is a 'window'... but obviously not used as I have sidelights in the indicators! Brilliant.

Final question, are 'either side' interchangable or is there a fixed left and right hand light?

[Alec]

Hello Arthur,

they are interchangeable.

Alec

[simmitc]

Although it may seem "unmorris", sealed beam units are indeed more reliable than separate bulbs. They are also plentiful and cheap. I expect to pay about £5 - £7 for a sealed beam unit, but halogen or other high output bulbs can be two or three times that. If you want to use the small window to mount an additional sidelight bulb then there is no reason why you shouldn't - personal choice.

When looking at the three pin connector on the sealed beam, one terminal is a common earth. The others are one each for main and dip. If you get them mixed up then you won't get everything working. There is a special connector that fits directly on, but if you are on a budget, then normal female blade terminals will fit - go for insulated ones.

[kennatt]

you seem to be a bit confused as to what a sealed beam unit is ,it is basically a large bulb shaped to fit onto the headlight unit,forget about separate bulbs .and no not all units will fit because some have a different shape on the lip to fit different headlight bowls,for instance the mgb ones will not fit the morris bowls(Don't ask why I know),Look closely at the filament and work out which terminal is the common earth, can't remember but think its one of the side ones not the one at the top someone will know ,take this to the earth side of you car then run a cable from positive terminal on battery, asume you have negative earth and touch each of the other terminals to check the unit.if no light throw it away and buy a new one.Last one I got was £25 from tom roys,but I understand that they are no longer being produced so will eventually become short supply.

[simmitc]

For sealed beam units, see see http://www.vehicle-wiring-products.eu/V ... dlamps.php part number 7014 £9.51 plus post & vat - gone up a little bit from when I last purchased, but no supply problems at the moment.

[Arthurdaily]

Hi, no I get it now - what was confusing me in the end turned out to be the fact they are different headlights, ie odd ones on the saloon!!!