Truck lighting question

[Jdbillin]

Hi, I am currently in the process of rewireing a truck. The only factory pieces I'm reusing is the lights and the switches. I figured out what wires I need to use for the switches a ran all the wireing and I went to test it and everything worked as it should except the brake lights. All the running lights worked as they should and the turn signals worked. I traced the problem for the brakes to a broken wire. Once I repaired it all the lights worked fine as long as the brakes were off. As soon as you hit the brakes the front running lights come on and the turn signals do not flash. But as soon as you let off the brakes everything works as it should. So my question is do I need to put a diode on the brake lights to keep them from back feeding to the rest of the lights? If so what kind of diode should I get and were exactly should I put it?

Thanks
Jordan

 

[CocaCola]

99% of all brake lights are a simple closed loop with a mechanical switch on the peddle control arm under the dash... You should not need any diodes you have something wired funny with the brakes and it's feeding backwards into another circuit...

 

[Jdbillin]

Hmm. I bacially started from scratch on the wireing. I used one power wire for all the exterior lights and just branched off of it for the brake switch and turn signal switch. Then I put the headlights on a relay. I used a common ground for all the lights to. I've doubled checked everything and it all works until the brake pedal is pressed. Any idea were I should start at as far as trouble shooting it?

Thanks
Jordan

 

[davenn]

Hmm. I bacially started from scratch on the wireing. I used one power wire for all the exterior lights and just branched off of it for the brake switch and turn signal switch. Then I put the headlights on a relay. I used a common ground for all the lights to. I've doubled checked everything and it all works until the brake pedal is pressed. Any idea were I should start at as far as trouble shooting it?

Thanks
Jordan

remove the brake light supply from out of the wiring for the other lights, DONT have it common with anything else

Dave

 

[duke37]

Many problems with vehicle lights are due to faulty grounds.
If some other lights come on when the brake lights are activated, then these are providing the groumd connection for the brake lights.
Check the ground to chassis voltage of the brake lights in the various conditions. It should always be close to zero.

 

[Jdbillin]

remove the brake light supply from out of the wiring for the other lights, DONT have it common with anything else

Dave

So do I need to run another seperate power wire from the battery to the brake light switch?

 

[davenn]

So do I need to run another seperate power wire from the battery to the brake light switch?

That would be my suggestion and along with that follow duke37's advice about faulty ground connections

Dave

 

[Jdbillin]

That would be my suggestion and along with that follow duke37's advice about faulty ground connections

Dave

Ok I will give that a try. I'm not trying to be ingorant but whats the reason behind running a seperate power source? Isn't 12 volts 12 volts?. I will also check all the grounds. I don't think there will be an issue there cause I ran every ground wire back up to a common ground under the dash.

Thanks
Jordan

 

[duke37]

But is the common ground solidly connected to chassis? Take a wire from here and check that it is always 12V away from the battery positive or 0V away from battery negative.

 

[CocaCola]

But is the common ground solidly connected to chassis?

I have seen a lot of people remove or 'forget' to replace the backup ground to chassis cable when they have done engine swaps and/or other major car renovations... For good measure there should be a flat braided wire from the engine block to the firewall, and a failsafe negative battery terminal should also branch off and connect to the engine... There is also likely the primary ground from the battery to the chassis as well... At least this is the way most cars I have seen are configured so that there is redundancy in the ground...

Also are you using the correct bulb filaments for the 'brake' light, and not reverse feeding into the 'driving' light filament loop?

 

[Jdbillin]

But is the common ground solidly connected to chassis? Take a wire from here and check that it is always 12V away from the battery positive or 0V away from battery negative.

I have it set up to we're there is 2 studs on the firewall I'm connecting everything electrical to them. Ones positive and ones ground. They both have cables going directly to the battery. I'm almost positive it's not a ground issue cause other electrical stuff on the truck works to

I have seen a lot of people remove or 'forget' to replace the backup ground to chassis cable when they have done engine swaps and/or other major car renovations... For good measure there should be a flat braided wire from the engine block to the firewall, and a failsafe negative battery terminal should also branch off and connect to the engine... There is also likely the primary ground from the battery to the chassis as well... At least this is the way most cars I have seen are configured so that there is redundancy in the ground...

Also are you using the correct bulb filaments for the 'brake' light, and not reverse feeding into the 'driving' light filament loop?

The bulbs are the factory duel filament bulbs

 

[CocaCola]

The bulbs are the factory duel filament bulbs

I assumed as much, thus the reason I asked if you are using the correct filaments for the individual circuits as to not back feed one circuit into anohter... If you double up a filament and it bridges to another circuit you can get all sorts of interesting results...

 

[davenn]

I assumed as much, thus the reason I asked if you are using the correct filaments for the individual circuits as to not back feed one circuit into anohter... If you double up a filament and it bridges to another circuit you can get all sorts of interesting results...

so true
which is exactly why I recommended separate cabling for the brake lights

Dave

 

[Jdbillin]

I assumed as much, thus the reason I asked if you are using the correct filaments for the individual circuits as to not back feed one circuit into anohter... If you double up a filament and it bridges to another circuit you can get all sorts of interesting results...

Correct me if I'm wrong but arnt the factory bulbs already doubled up? One filament for the running lights and the other is for the brake/turn lights?

 

[CocaCola]

Review this page, there is not single right way to do it but this page might give some insight...

http://stores.homestead.com/ez2wire/Page.bok?template=turnsignal_faq

Also useful would be for you to scribble out the wiring diagram you have in place, I highly suspect you have a bridge somewhere that is back feeding to another circuit...

 

[duke37]

Have you connected the brake light 'upside down' so that when it is lit it also supplies power to the other lights? Check that the bulb outer is always at ground.

 

[Jdbillin]

I kinda wrote up a quick diagram of what I'm doing. I'm not sure how to post it though

 

[(*steve*)]

I kinda wrote up a quick diagram of what I'm doing. I'm not sure how to post it though

Save it as a jpg.

When you're writing your post, press the "advanced" button, then use the icon which looks like a paper clip.

You use this to locate the image, then upload it.

A thumbnail will appear with your post that people can click on to view.

Beware that there are size limits of what you can attach.

 

[Jdbillin]

hopefully that worked

 

[davenn]

hopefully that worked

well sorta

very difficult to read, how about drawing it in paintbrush, crop it to a nice size 640x480 or smaller and saving as a gif then post it

its going to be much easier to see what is going on
but at least you got the posting of an image sorted out

cheers
Dave