12v Headlight problem
 

I bought a set of 7" 12v headlights and found the hi and low beam filaments joined instead of being two separate filaments with a common ground. The result when applying voltage to the hi beam filament, voltage became available at the low beam filament contact as well. And visa versa.

The only solution is to use a relay to power hi and low beams. Wiring directly to the headlight just as the 6v lights were wired causes the red dash hi beam indicator bulb to light in both hi and low positions. BTDT

My question is regarding the bulb filament. Has anyone ever gotten into a 12v sealed beam to understand the physical difference of between a 6v and a 12v bulb filament?

Re: 12v Headlight problem
 

Positive or neg ground? I'm no electrical engineer but I'm guessing that the ground is mixed up.

Re: 12v Headlight problem
 

I have installed 12 volt sealed beams as a replacement for 6 volt sealed beams.
The original 3 prong 6 volt receptacle is identical to the 12 volt.
There should not be any issues with high/low beam function.
I suspect that if any wiring was replaced or altered, that is where the problem exists.
Also check the wiring and functionality of the dimmer switch.

Re: 12v Headlight problem
 

This diagram shows the socket function. The High and low beam filaments are connected to a common ground. There will be a problem only if one of the headlights loses a ground. The power will back feed to the other lamp to seek a ground. this is the same for both 6v and 12v.

Re: 12v Headlight problem
 

I'd check for a bad ground.

Re: 12v Headlight problem
 

Bad grounds account for "bewildering" things happen. One of them is that the tail light will work on both sides, but when you step on the brake, only one will work and the tail light on the other side will go out.

Re: 12v Headlight problem
 

I put a 12v 7" sealed beam bulb on a clean workbench with a 12v battery and voltmeter. Connect battery -12v to the ground terminal of the bulb per diagram above and +12v to the hi beam terminal. The lamp lights and +12v comes out of the low beam terminal enuf juice to light another bulb.


Nothing to do with grounds or old wiring. I'm interested in knowing why when I apply voltage to either hi or low beam terminals, voltage appears at the other terminal.
If I apply voltage to a 6v bulb NO VOLTAGE appears at the other terminal.


Guys, if a chicken died in the back seat of an '35 Ford at 25mph, someone would claim it had a bad ground. Please concentrate on the 12v bulb if you have ever messed with one. (and forget ground)



Thanks 41F1 for the nice socket diagram.

Re: 12v Headlight problem
 

I'd try another bulb or manufacturer.
Paul in CT

Re: 12v Headlight problem
 

Just did the same procedure ( without the clean workbench)
This is with a Sylvania H6024 halogen sealed beam, high beam on, ZERO voltage from the low beam terminal.
At this point it sounds like an anomaly with the bulb.

Re: 12v Headlight problem
 

I had a set of those Sylvania Halogen bulbs some years ago in a 280Z.
On low beam, only the low beam filament lit up. On high beam, both filaments lit up. Brighter lights that way and if I remember correctly, they were advertised to do that.
Ken

Re: 12v Headlight problem
 

What lamp numbers are being tested? Unless there is some internal component, such as a diode, I'm not sure how both filaments would come on at the same time on high beam and not on low beam. You have to consider that I am analysing this as mechanic. The manufacturer may be using the same principal as used for three-way lights in your living room, to get a brighter headlamp.


How do you get three levels of lighting with two filaments?
Low = 50W
Med=100
High= 150W (two filaments 50+100 on at the same time, controlled by the switch)

Re: 12v Headlight problem
 

that image posted above is looking at the front, or open end of the plug, now looking at the rear of the bulb is a mirror image, ground on the left, high on the right. is that how you hooked up your test?

Re: 12v Headlight problem
 

Thanks - I'm going to rebuy some bulbs (Sylvania H6024) as it sounds like I got a pair of strange ones.

Re: 12v Headlight problem
 

I finally got around to finishing the research, starting with purchase of a Sylania H6024. Sorry but I don't recall the manufacturer of the near idential bulbs with problems. Recall those problem was that the dash speedometer RED hi beam indicator light, lit on both hi and low beams positions. I'm a mile away from my garage and will get the mfgr data later (and post it here).


Bottom line, the Sylvania has totally indepentant halogen high and low beams filaments within the bulb. The generic over-the-counter halogen 7" blub have a common something so that when applying voltage to ground and low beam terminals, 12v squirts from the high beam terminal as well even though no voltage was sent to that terminal from the switch.


Time to order a matching bulb for the other side.

Re: 12v Headlight problem
 

Couldn't resist, that sounds like a grounding problem! :D

Re: 12v Headlight problem
 

And I'd hate to be that chicken in the back seat! Terry

Re: 12v Headlight problem
 

Here is a picture of a 12v headlamp wiring.

click on picture to Enlarge ;)

Re: 12v Headlight problem
 

when you are on low beam one filerment is lit when you go to high beam both filerments are lit.

Re: 12v Headlight problem
 

Not usually.

Re: 12v Headlight problem
 

On my '65 Fastback, when the lights are on dim, Only the dim wire has power.
When the headlights are on bright, Only the bright wire has power.
And Only one filement lights up at a time.


.