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Combined signal, brake and tail light

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3Ds

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Hello all,
I'm restoring an old truck which has a 6 volt positive ground electrical system. I am replacing the lights with LED arrays and need some advice to drive them.
I've attached my proposed circuit but think there will need to be some diodes or at least with all the switching maybe some snubbers however it is confusing to me being a positive ground vehicle and me being new to electronics.
I would really value any advice.
Thanks
 

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Welcome, 3Ds!

How did you arrive at the resistors' values?

What info can you provide on the LEDs (either as singles or arrays)? How did you arrive at the total number of LEDs (I can't make your totals work)?

Are the TAIL light LEDs (STOP and TURN, I'm assuming) really wired as you show, since in either LEFT or RIGHT usage, they'll both light up simultaneously, no matter which switch is closed)?

Yes, you should add snubber diodes across the coil(s) of the relays. Please provide some info on the relays.
 
I'm going to give you some hints. The ground symbol has to go, but I admire you TRYING really hard to convey the positive ground notion. Use the open triangles that point UP. That will designate that it's a common. For like -6 just use an arrow. e.g. -BAT or -IGN.

Just a note: I tend to over think. Any idea is worth presenting.

There is definitely something wrong with the RF LED and RL1b

If you hunt around, you may find 6V automotive LED lamps. You might find it easier to work with it as a negative ground system and then flip it. The standard flasher won;t work. You'll have to create one. It used power draw of the lamps and heating, You had an added effect, when a lamp or more burned out the blinkers won't flash. The flasher also has to make NOISE.

I see two options 1) relay/diodes/flash module and 2) Your own sort of BCM module and 3) A BCM module with lamp fail detection. You could look at www.picaxe.com . Again, not your question,

Four way flashers is an option and so is the third brake light. There were kits to add 4-ways way back when and there were kits to add a third brake light. JC Whitney comes to mind. I think they used like a 4PDT slide switch and a separate flasher, but do brake lights override?

So relays of the SPDT. DPDT or ever 4PDT could be used in your design, with diodes doing ORing of signals and for coil transient suppression.

That said, it's a complex beast if you include 4 ways and a 3rd brake light. You didn't.

I'd look at the design as:
The turn signals overide for the front. Blinking is LEFT or RIGHT sides of the car. e.g. left turn, right turn
so, you get; the parking light circuit provides the power to the front lamp if not blinking.

and you get

The brake circuit provides power to the brake lamp if not blinking for the rear.
parking is a separate bulb. Corrolary: You need to provide a LEFT and RIGHT brake signal from the single brakes signal.

4-way flashes left and right sides. Brake overides rear bulbs or a per bulb basis.

Third brake is from left or right brake. i.e. you might have to separate the brake signal into left brake and right brake. because the turnsignals are operating the "sides" of the car,

That does mean you'll have to come up with some logic to direct the turn signals and select/de-select the hazzard mode and provide flash and make noise.

So, the key is creating left an right brake signals which are compatible with left turn/right turn,

One other headache is that Hazard is powered from -BAT and turn from -IGN OR -IGN disables turn.
 
I tried to make some sense from here as to what was the norm: http://chevy.oldcarmanualproject.com/electrical/wiring/

So, frankly, I would just use either large circles or arrows, e.g. an arrow pointing to -IGN.

and the same for +BAT. I would put the symbol of chassis (ground) at the battery source once, I Think, because in reality only the bonded wires to chassis are connected to chassis. Your circuit would be independent until one point. Modern cars actually have ground wires and don't depend on the chassis.
 
Welcome, 3Ds!
Thank you
How did you arrive at the resistors' values?
The rear light isn't drawn properly. 2 LEDs should be in series and there are 22 sets per light. (I've attached some photos)
What info can you provide on the LEDs (either as singles or arrays)? How did you arrive at the total number of LEDs (I can't make your totals work)?
The truck peaks close to 8 volts. LEDs are 2.1v 20mA.
Are the TAIL light LEDs (STOP and TURN, I'm assuming) really wired as you show, since in either LEFT or RIGHT usage, they'll both light up simultaneously, no matter which switch is closed)?
Yes I would like all the LEDs to function together for both stop and turn. Also for park lights but at at lower intensity
Yes, you should add snubber diodes across the coil(s) of the relays. Please provide some info on the relays.
The relays Are Panasonic TQ2SA-6V and HY1Z-6V.
Thanks for your response
 

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I'm going to give you some hints. The ground symbol has to go, but I admire you TRYING really hard to convey the positive ground notion. Use the open triangles that point UP. That will designate that it's a common. For like -6 just use an arrow. e.g. -BAT or -IGN.
Thanks, I just tryed to use some std symbols from the library. I've never used Design Spark software so I have a steep learning curve...
Just a note: I tend to over think. Any idea is worth presenting.
I appreciate your over thoughts...
There is definitely something wrong with the RF LED and RL1b

If you hunt around, you may find 6V automotive LED lamps. You might find it easier to work with it as a negative ground system and then flip it. The standard flasher won;t work. You'll have to create one. It used power draw of the lamps and heating, You had an added effect, when a lamp or more burned out the blinkers won't flash. The flasher also has to make NOISE.
The lights themselves are custom made to hold the LEDs and fit inside the old housings. I didn't shown the flasher but will pick up an electronic 6 volt motorcycle flasher or add some resistance in series. The circuit is just for me to prove out a way to use all the LEDs in the array without having some light up for each function.
I see two options 1) relay/diodes/flash module and 2) Your own sort of BCM module and 3) A BCM module with lamp fail detection. You could look at www.picaxe.com . Again, not your question,
I did try using a commercially made product for combined trailer lights run from a modern car with separate signal and brakes. It didn't work with reverse polarity.
Four way flashers is an option and so is the third brake light. There were kits to add 4-ways way back when and there were kits to add a third brake light. JC Whitney comes to mind. I think they used like a 4PDT slide switch and a separate flasher, but do brake lights override?
The 4 ways are handled in the signal light switch. Sorry I didn't show that in the circuit as it is existing.
So relays of the SPDT. DPDT or ever 4PDT could be used in your design, with diodes doing ORing of signals and for coil transient suppression.

That said, it's a complex beast if you include 4 ways and a 3rd brake light. You didn't.
No 3rd brake light either. Shes 65 years old and I just want it to look original even though they didn't come with signal lights either ...
I'd look at the design as:
The turn signals overide for the front. Blinking is LEFT or RIGHT sides of the car. e.g. left turn, right turn
so, you get; the parking light circuit provides the power to the front lamp if not blinking.
Don't need park lights for the front. They exist separately.
and you get

The brake circuit provides power to the brake lamp if not blinking for the rear.
parking is a separate bulb. Corrolary: You need to provide a LEFT and RIGHT brake signal from the single brakes signal.

4-way flashes left and right sides. Brake overides rear bulbs or a per bulb basis.

Third brake is from left or right brake. i.e. you might have to separate the brake signal into left brake and right brake. because the turnsignals are operating the "sides" of the car,

That does mean you'll have to come up with some logic to direct the turn signals and select/de-select the hazzard mode and provide flash and make noise.
I will mount all these relays under the dash so there may be some noise there.
So, the key is creating left an right brake signals which are compatible with left turn/right turn,

One other headache is that Hazard is powered from -BAT and turn from -IGN OR -IGN disables turn.
Not sure what you mean here.
Thanks for your help.
 
I tried to make some sense from here as to what was the norm: http://chevy.oldcarmanualproject.com/electrical/wiring/
Cool site. The 46 truck is pretty close.
So, frankly, I would just use either large circles or arrows, e.g. an arrow pointing to -IGN.
I'll try and fix up the symbols but the circuit is just for my use and I do struggle with the software.
and the same for +BAT. I would put the symbol of chassis (ground) at the battery source once, I Think, because in reality only the bonded wires to chassis are connected to chassis. Your circuit would be independent until one point. Modern cars actually have ground wires and don't depend on the chassis
Thanks
.
 
Sorry my pictures didn't come out right previously
 

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Also, here are some photos of the front light. The center 4 LEDs are for the park lights and are not included in the attached circuit.
 

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Wow. Looks nice, but I'm not sure if you missed the boat with LED design.

Here https://www.avagotech.com/docs/AV02-2459EN is just a datasheet. Stuff of interest is Vf max, the intensity vs ambient temperature and nominal If (or Test conditions).

So typical is 20 mA and not more than 50 mA with a max Vf of 2.4 V. So for a single LED operating on 6V, you would need a series R of (6-2.4)/20e-3 = 180 ohms nominal and you may have done that. You could only put two LEDS in series (6-2.4-2.4)/20 mA. One LED would offer slightly better performance. You can check the wattage too. The color of the LED influences the nominal Vf.

Your LED housing is going to need a way to vent heat and probably there are intensity standards to meet, LED lamps in newer vehicles seem to be more discrete where replacement lamps are more omni-directional to take advantage of the reflector. A solar cell at short circuit current is a great way to monitor intensity. Watch the viewing angle as well.

Using current control gives you a better handle on intensity variations. Don't put LEDs in parallel.

This vehicle might not have even had turn signals for all I know.

So, concerned based on your pics.
 
The relays probably take more current than the LED's . Are you using existing wiring?

  • The RED or YELLOW HB 5mm 30 deg 5000~10000 mcd LEDs will be 2.0~2.2V each @ 20mA
  • Choose 492nmD f0r Amber and 540nmD for Red
  • Check your alternator voltage., It should be 7.1V running and 6.3V off and 5.7V with a low battery.
  • You can use 2 or 3 in series with parallel arrays.
  • Consider a dozen LEDs per array or 6x 20mA per string of two for more constant brightness.
  • You can run a string of 3, but the lights may reduce brightness with generator voltage at idle like old headlights.
  • Thus the series R for each 60mA string of two LEDs at 4.4max is 2.7V/0.06A= 45R 1/4W
  • Worst case when the engine is off, emergency flasher on brake lights with a dead battery at 5.7V would take (5.7-4.4)/45R about 30mA or half brightness
  • 524nmD is a light Red and needs filtering in lens than a 540nmD deep Red.
  • Intensity is always greater in narrow lens but for 30 deg (+-15) can range from <1000 to 10000 mcd. Go for the best.
If you can't find any, I have Amber LEDs in bags of 500 pcs 10,000 mcd 30 deg 492nm Y dominant colour, 2.1V. mine are all matched so you can run them in parallel.
 
Wow. Looks nice, but I'm not sure if you missed the boat with LED design.
Thanks for your interest
Here https://www.avagotech.com/docs/AV02-2459EN is just a datasheet. Stuff of interest is Vf max, the intensity vs ambient temperature and nominal If (or Test conditions).

So typical is 20 mA and not more than 50 mA with a max Vf of 2.4 V. So for a single LED operating on 6V, you would need a series R of (6-2.4)/20e-3 = 180 ohms nominal and you may have done that. You could only put two LEDS in series (6-2.4-2.4)/20 mA. One LED would offer slightly better performance. You can check the wattage too. The color of the LED influences the nominal Vf.
The trucks voltage peaks close to 8V so I used a little bigger resistor. The amber LEDs are HLMP-EL1B-Z1KDD and the Red LEDs are C503B-RAN-CY0B0AA1
The front lights are in the truck now and seem plenty bright. It doesn't have to meet any D.O.T. standards as all the truck originally came with was hand signals.;)

Your LED housing is going to need a way to vent heat and probably there are intensity standards to meet, LED lamps in newer vehicles seem to be more discrete where replacement lamps are more omni-directional to take advantage of the reflector. A solar cell at short circuit current is a great way to monitor intensity. Watch the viewing angle as well.
Again, brightness and intensity aren't a big issue for me but heat may be. It isn't likely this truck will even be driven in the dark but I guess I don't want a meltdown...
Using current control gives you a better handle on intensity variations. Don't put LEDs in parallel.
The drawing with the LEDs in parallel was just my cad error. I plan to use 2 in series in the back lights. The fronts are individual.
This vehicle might not have even had turn signals for all I know.
Nope.
Thank you for your input.

So, concerned based on your pics.
 
The relays probably take more current than the LED's . Are you using existing wiring?
The wiring will be new
  • The RED or YELLOW HB 5mm 30 deg 5000~10000 mcd LEDs will be 2.0~2.2V each @ 20mA
  • Choose 492nmD f0r Amber and 540nmD for Red I've purchased amber LEDs are HLMP-EL1B-Z1KDD and the Red LEDs are C503B-RAN-CY0B0AA1
  • Check your alternator voltage., It should be 7.1V running and 6.3V off and 5.7V with a low battery. It has a generator but that sounds about right although I did see spikes close to 8V
  • You can use 2 or 3 in series with parallel arrays. I used singles in the front in case of component failure, I wouldn't loose 2 LEDs and in the back I will pair up 2 in series. I don't think I have enough voltage for 3.
  • Consider a dozen LEDs per array or 6x 20mA per string of two for more constant brightness. I'm limited to 9 in the front because of the housing size and have 44 in each rear light.
  • You can run a string of 3, but the lights may reduce brightness with generator voltage at idle like old headlights.
  • Thus the series R for each 60mA string of two LEDs at 4.4max is 2.7V/0.06A= 45R 1/4W
  • Worst case when the engine is off, emergency flasher on brake lights with a dead battery at 5.7V would take (5.7-4.4)/45R about 30mA or half brightness
  • 524nmD is a light Red and needs filtering in lens than a 540nmD deep Red. I do have amber lenses in the front and red ones in the back.
  • Intensity is always greater in narrow lens but for 30 deg (+-15) can range from <1000 to 10000 mcd. Go for the best.
If you can't find any, I have Amber LEDs in bags of 500 pcs 10,000 mcd 30 deg 492nm Y dominant colour, 2.1V. mine are all matched so you can run them in parallel
Thank you very much, I already have all these mounted so hopefully they will work out.
Any thoughts on the circuit design?
 
I've corrected the LED circuit in the tail lights and added some part numbers.
Please have a look at the revised drawing.
Thanks again for all of your help.
 

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Do you want to consider a design that adds 4-way flashers and/or third brake light?

Thanks but the 4 way flashers are already built in to the signal light control on the steering column.
I think a third brake light would look out of place on a 1946 truck ;)
Thanks
 
I found some mistakes and also added the existing flasher for more clarity.
What size resistor should I use for R3 and R4 to get about half intensity from the LED array?
Would anyone care to comment on how I should use some diodes in this design?
Thanks

6 volt signal light circuit revised 4.jpg
 
I've been busy. I haven't been able to look at your circuit, but I did scribble down a potential circuit start starting from a 12V negative ground system, all because I'm more comfortable starting there. It might be a DPDT relay and two diodes that have to carry the full light current for each lamp. Park or brake may have to be inverted. Turn can be either.

I'm struggling with a migraine and other stuff to do.

Quickly:
What do logic sense does the car have to have for for 6V pos ground:
Brake: any, switch to chassis turns on brake, switch to -Bat turns on light.
The same questions for:
Turn
and Park.

I designed based on left side/right side turn. Brake overrides turn for rear lamps. Turn overrides park for front lamps. Front park and front turn are identical, right?

Not sure I have it right yet.
 
Since I don't have an easy way of drawing, I'll have to talk out a 12 V negative ground system. It basically consists of a DPDT relay for each light

NOa is Normally open, a side; NC - Normally Closed; C= Common
There is also a b side.

NOa goes to nothing
NOa goes to the cathode of a diode and then to +12 ign
Ca goes to the lamp and to NCb
The other side of the lamp goes to ground
Cb goes to the negative side of a diode to (L Brake, R-brake or LF Park or RF Park)*

Describing the brake system. At the brake switch (switched +12), it will branch to two diodes, the same diodes as in the description above, so we get a left and right brake signal that's independent.

If the turn signal is not on, the flow will be from the brake switch to the lamp.
If the turn signal is ON and the brake light is off, power would flow from the IGN terminal to the lamp through the NOa contact.
If the brake and turn signal are on, The light would get power through the brake switch until the turn signal switched, then t would get power from the diode side of the IGN terminal.

The relay coils are arranged such that the left or right sides are connected in parallel.
Two diodes give a left and right brake light.

This is a 12 V neg ground and assumes that 12 V is switched from brake and 12 V is switched for Park. Turn is easy to switch. Should be easy to change to 6V. there should be reverse biased across the relay coils as well. Turn is suppled from an IGN source and a Bat source, but doesn't have to be. Only the coils need to be powered from an IGN source,

Park is arranged the same way. Turn overrides park. Park also has two diodes for the front lamps.
 
Last edited:
Wow, thanks for all your work. I can't imagine looking at a computer screen can be too good for a migraine.
In the spirit of keep it simple... I did a search on trailer wire converters and found lots of examples of circuits doing what I need. I will have to change them to 6 volt and positive ground of course. Many of them use the same basic design I was suggesting although use automotive 12v relays which I don't think will work reliably on 6 volts either.
As a visual guy I'm having a little trouble working out your schematic but I'm very impressed you can do that in your head. No wonder you have a headache...
I designed based on left side/right side turn. Brake overrides turn for rear lamps. Turn overrides park for front lamps. Front park and front turn are identical, right?
No turn would override brake but only on the active side.
There is no park circuit to the front lights and probably should be disregarded for the rear lights as it isn't an issue and muddies up the project
Thanks again.
 
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