The Ford Barn

flathead34 · 08-09-2023, 04:20 PM

On our '34, when we have the brake lights on and then when the headlights are turned on the brake light goes off. This only happens on one brake light, the other performs normally. In studying this problem, we observed that only one filament was being used by both. We changed out numerous double-filament bulbs and they all performed the same, the brake light and the head light used that same filament on that side. What do we have to do to correct that and not have that brake go off when the headlights are on?

Bob C · 08-09-2023, 05:51 PM

Are you sure it's the brake light and not the tail light that's going out?
If it's the tail light it could be a grounding problem. Only one head light filament
should be on at a time. One filament is low beam and the other is high beam.

paul2748 · 08-09-2023, 06:58 PM

It sounds like a grounding problem. Run temporary grounds to each taillight housing and see if that solves the problem

JayChicago · 08-09-2023, 08:48 PM

Really confusing when you say headlights when you are talking about the taillight. Yes headlights and taillights come on together, but the headlights have nothing to do with this problem.

As said above, this is a classic symptom of no ground at the bad light's socket. Brake light is using the taillight filament and wiring to find ground at the other side's good socket. Only the taillight filament lights up because it is smaller. And then this strange path to ground gets blocked when taillights have power on.

To fix this, look at how the socket is attached. Needs clean, tight, metal-to-metal contact between the socket and truck body. Sometimes it's a coat of paint breaking the contact.

big job · 08-10-2023, 05:32 AM

Your best friend is a simple test light

Terry,OH · 08-10-2023, 06:16 AM

Sponsored Links (Register now to hide all advertisements)

Sounds like the problem is the connections or grounds to the one light that goes off. What light bulb are you using? the brake light is just one filament of the dual filament light bulb with the tail light being the second.

flathead34 · 08-10-2023, 09:45 AM

Thank you guys for your responses We will look at the grounding. There is some confusion the way I described the problem when we turned the headlights on. We step on the brake pedal and the brake lights come on. With brake lights on we turn on the headlights. One brake light turn off. Do you think this happens because improper grounding on that one tail light? The other brake light works properly with the headlights on.

Bob C · 08-10-2023, 10:25 AM

The most likely cause is a bad ground.

JayChicago · 08-10-2023, 10:45 AM

Quote:

Originally Posted by flathead34

Do you think this happens because improper grounding on that one tail light?

Yes. That is what everyone here is saying.

flathead34 · 08-10-2023, 01:01 PM

Thanks for all you help. Off to find the ground problem

08-09-2023, 04:20 PM	#1
flathead34 Senior Member Join Date: May 2010 Location: Oro Valley, AZ Posts: 435	Brake Lights Dilemma On our '34, when we have the brake lights on and then when the headlights are turned on the brake light goes off. This only happens on one brake light, the other performs normally. In studying this problem, we observed that only one filament was being used by both. We changed out numerous double-filament bulbs and they all performed the same, the brake light and the head light used that same filament on that side. What do we have to do to correct that and not have that brake go off when the headlights are on?

08-09-2023, 05:51 PM	#2
Bob C Senior Member Join Date: May 2010 Location: So Cal Posts: 8,754	Re: Brake Lights Dilemma Are you sure it's the brake light and not the tail light that's going out? If it's the tail light it could be a grounding problem. Only one head light filament should be on at a time. One filament is low beam and the other is high beam.

08-09-2023, 06:58 PM	#3
paul2748 Senior Member Join Date: May 2010 Location: Midland Park, NJ Posts: 3,982	Re: Brake Lights Dilemma It sounds like a grounding problem. Run temporary grounds to each taillight housing and see if that solves the problem __________________ 48 Ford Conv 56 Tbird 54 Ford Victoria

08-09-2023, 08:48 PM	#4
JayChicago Senior Member Join Date: Jan 2019 Location: Chicago Posts: 732	Re: Brake Lights Dilemma Really confusing when you say headlights when you are talking about the taillight. Yes headlights and taillights come on together, but the headlights have nothing to do with this problem. As said above, this is a classic symptom of no ground at the bad light's socket. Brake light is using the taillight filament and wiring to find ground at the other side's good socket. Only the taillight filament lights up because it is smaller. And then this strange path to ground gets blocked when taillights have power on. To fix this, look at how the socket is attached. Needs clean, tight, metal-to-metal contact between the socket and truck body. Sometimes it's a coat of paint breaking the contact. Last edited by JayChicago; 08-10-2023 at 02:01 AM.

08-10-2023, 05:32 AM	#5
big job Senior Member Join Date: Sep 2013 Location: Dighton, Mass Posts: 1,230	Re: Brake Lights Dilemma Your best friend is a simple test light

08-10-2023, 06:16 AM	#6
Terry,OH Senior Member Join Date: May 2010 Posts: 4,751	Re: Brake Lights Dilemma Sponsored Links (Register now to hide all advertisements) Sounds like the problem is the connections or grounds to the one light that goes off. What light bulb are you using? the brake light is just one filament of the dual filament light bulb with the tail light being the second.

08-10-2023, 09:45 AM	#7
flathead34 Senior Member Join Date: May 2010 Location: Oro Valley, AZ Posts: 435	Re: Brake Lights Dilemma Thank you guys for your responses We will look at the grounding. There is some confusion the way I described the problem when we turned the headlights on. We step on the brake pedal and the brake lights come on. With brake lights on we turn on the headlights. One brake light turn off. Do you think this happens because improper grounding on that one tail light? The other brake light works properly with the headlights on.

08-10-2023, 10:25 AM	#8
Bob C Senior Member Join Date: May 2010 Location: So Cal Posts: 8,754	Re: Brake Lights Dilemma The most likely cause is a bad ground.

08-10-2023, 01:01 PM	#10
flathead34 Senior Member Join Date: May 2010 Location: Oro Valley, AZ Posts: 435	Re: Brake Lights Dilemma Thanks for all you help. Off to find the ground problem