Headlight Mystery

[mabryt]

Hi all-

Here's a weird one.

All of a sudden, my left front (i.e. Yank driver's side) low beam headlight seems to have burned out.

But on closer inspection, it has NOT burned out.  I know this because when I hit the high beams, BOTH the high and low beams turn on.  But the low beam only goes on when the high beam is on as well.  Otherwise, only the right front low beam is lit and I've got a one-eyed car.

I checked the spade connectors on the lamps- all fine.

I checked all the fuses just in case- all fine.

What gives??

[koan]

What gives??

You have lost an earth connection on one of the head lamps.

I'm thinking... Do you have euro or US headlamps?


koan

[mabryt]

Hi Koan-

I have US headlamps.  The connections at the back of the lamps are intact- should I follow the wires and look for a break somewhere?

Much appreciated-

TJM

[koan]

I have US headlamps.  The connections at the back of the lamps are intact- should I follow the wires and look for a break somewhere?

Follow the earth  wires (usually brown) from the head lamp sockets to where they connect to the body. My wiring book says the grounds are at the "left side of radiator".

This sort of thing can happen with any sort of twin filament lamp, the filaments have a common earth, if that is open circuit there is a"sneak" path to earth/ground via the second filament and the matching lamp on the other side.

Are you sure the fuses are OK?  There are 4 of them for the headlights.  Are all the fuses in properly, none leaning to one side touching the adjacent fuse?

The opposite to what you describe is what usually happens with earth problems.  A light is on, maybe a bit dim and it goes out when head light stalk is flashed to put both high and low beams on but I can't think of any thing else but earths.

koan

[nim205]

If you look at the wiring diagram around section 22, you'll see that the high beam plus feeds both high and low beems, while an additional low beam plus feeds the low beam alone. Your break should be along this wire from the lighting unit to the relay switch.

I'd start checking the 16A fuse for this light (#F14 - replace, not only visual inspection) then locate the wire itself and check for continuity. If this fails, move on to the relay.

Good luck,

Nimrod

[Papalangi]

US lamps have two filaments in the outside (or upper if stacked) lamp. One for low beam and one for high beam.  They do not use both at any time.

The high beam, inboard or lower lamp, has one filament and comes on only as a high beam.

You have a burned out low beam filament.

You need to replace the whole shebang if it's sealed or just the bulb if it's a non-sealed halogen type.

You can also try smacking it hard with your fist while it's on.  Every third or fourth try, it works for me.  Doesn't last long though.

Michael

[mabryt]

Much appreciated everyone-

I'm picking up a spare lamp anyway so will give it a go, but will also check the ground wires.  As for fuses, they all appear intact- but do fuses get weaker as they get older?  Hmmm.

Thanks-

TJM

[TJ 450]

Sometimes, the contacts of the fuses can corrode, so it might be worthwhile either cleaning the contacts with a pencil eraser or turning the fuse back and forth in position.

Tim

[koan]

US lamps have two filaments in the outside (or upper if stacked) lamp. One for low beam and one for high beam.  They do not use both at any time.

They do if the stalk is pulled to flash which is what I assume "hit the high beams" meant.

If maybt assumed all the lamps are single filament, a burnt out low beam in the high/low lamp could be the problem.

koan

[Papalangi]

US lamps have two filaments in the outside (or upper if stacked) lamp. One for low beam and one for high beam.  They do not use both at any time.

They do if the stalk is pulled to flash which is what I assume "hit the high beams" meant.

If maybt assumed all the lamps are single filament, a burnt out low beam in the high/low lamp could be the problem.

koan

Forgot about that.

Yes, all six filaments will light up if you hit the flash to pass.

Also, my statement only applies to the older US style separate globe type headlights whether round or rectangular.

Michael

[John Hubertz]

Hey, check your stocks, business opportunities and lost lusts -

Cuz nobody that is left out gets the real premium fun....

...and once you aren't left out, you'll be IN MAN IN

Go for it - when in doubt - flip it out, and the bulb may look fine but
test - like a hot girl you've gotta make sure you've got continuity to
light her up.  Lookin ready and lighting up are two different concepts
for both lamps and tramps.

Pull out that Ohm baba pointy tipped tester and put that source of
wild sunshine to good ground and when you touch it see if it goes O

LOL

[mabryt]

Hey Koan-

Right on the money.  I replaced the high/low sealed lamp and now everything works properly.  However, the new bulb uses a halogen-type filament and is so much brighter than the other old one that now I need to replace that one, too!

But looking good.  Thanks for the input.

T.