I bought a CURT custom wiring harness that plugs into vehicle tail light assembly to provide a 4-way flat socket. It has a simple plug&play design that eliminates the need for cutting and splicing of the car's original harness. It provides a wire for left turn/stop, a wire for right turn/stop, a wire for tail/side markers/license plate, and the 4th wire for the ground. Basically this 4-way socket was supposed to be used as in the diagram provided by this link.

The problem is that I am supposed to hook that socket into a trailer 7-way socket (ISO 1724).

Usually I am trying to avoid buying stuff that/if I can make as a DIY project.

Obviously I can bridge few of those 4-way socket wires to the 7-way socket:

• the white ground goes to the ground (pin #3 on the 7-way socket)
• the brown tail/license/side markers goes to the brown/black (pin #5 abd #7 on the 7-way socket)
• the green right signal/stop light goes to green (pin #4 on the 7-way socket)
• the yellow left signal/stop light goes to the yellow (pin #1 on the 7-way signal)

So far so good. But what about the brakes?

The 4-way provided assembly seems to use the same bulbs, both for turn signal and break/stop light. So when the car wants to signal it probably sends a intermittent voltage through that wire, thus blinking. When the car breaks it sends a continuous (non-intermittent) voltage through that wire to the same common-shared bulb (so we interpret that as "the break/stop light", because it does not blink). This make me think that with a 4-way wiring you cannot have both, the turn signal and break light at the same time, because these 2 functions share a common wire/bulb (as I said earlier, is the car that simulates these functions via intermittent/continuous voltage applied to the wire).

The 7-way socket (see ISO 1724) has a separate pin for brakes/stop lamps: the red pin #6.

So basically, the problem I have is to find how to connect the green/yellow wires from the 4-way socket to the pin #6 on the 7-way connector.

If we assume that we just take the yellow/green from the 4-way socket and to link them to the pin #6 it would mean that (1) the turn signal will behave like the emergency lights and nonetheless the stop lamps will do the same and (2) while braking both the turn signal lamps and the brake lamps will light.

OK, instead of using both the green/yellow 4-way harness wires to hook them to the pin #6 (brake) on the 7-way socket I could use a single one (let's say the Right). This means that while I am using the left turn signal it would be OK, while using the right turn it will flash both the right turn signal lamp but also the stop lights (which will look like the emergency lights). So this option is not working as well.

I don't see any simple solution (a wiring solution) to the problem above. The only way I know it will work is by the means of an electronic circuit that will take the advantage of the fact that the turn signal has a is intermittent voltage while the stop lights has a continuous voltage.

I am not in the electronics but I know how to solder a capacitor and a resistor or a diode to a PCB so I am open to any circuit design that would help me to solve this problem.

Any idea/hint/tips that could help me take the fog from my eyes? Thanks in advance for (1) you patience and (2) for your help.

 

On a standard vehicle with combination turn/park bulbs, switching between brake and turn signal is handled by the turn signal switch. The turn signal will still override the brake light on the side to which you are turning and allow the opposite side to act as a brake light.
To my knowledge, on most of the 7 wire connectors, the green and yellow wire still act as your left and right turn as well as your brake signal. Have you actually tested the receptacle to see if this is the case or do you know for sure that yours is connected differently in that it has a separate stop light signal? Sorry I have to ask but want to make sure we are clear. What type of vehicle are you working on?

 

You need to have a brake controller to power your trailer brakes. Simply putting 12 volts on them every time you touch the brake pedal of the tow vehicle is not the right way to go. Do a Google search of Brake Controller and you can get more information.

 

You might have the wrong converter: https://www.curtmfg.com/masterlibrary/01resources/appguides/Curt_Hitch_App_Guide.pdf

Ypur reference say not to bridge pins #5 an #7: https://en.wikipedia.org/wiki/ISO_s...pin_trailer_connector_Type_12N_.28ISO_1724.29

 

On a standard vehicle with combination turn/park bulbs, switching between brake and turn signal is handled by the turn signal switch. The turn signal will still override the brake light on the side to which you are turning and allow the opposite side to act as a brake light.
To my knowledge, on most of the 7 wire connectors, the green and yellow wire still act as your left and right turn as well as your brake signal. Have you actually tested the receptacle to see if this is the case or do you know for sure that yours is connected differently in that it has a separate stop light signal? Sorry I have to ask but want to make sure we are clear. What type of vehicle are you working on?

Probably you are right but as far as I know the ISO 1724 standards says stop lamps goes to the red wire, pin DIN 54 (or 6th). So on a 7-way socket it looks like the brakes have their own dedicated lamp which does not share its voltage with anyone. Btw, the car is a 2009 Nissan Murano.

For an unbraked trailer it would appear the 4 wire connector would be ok, for a trailer with electric brakes it doesn't seem suitable.

Was there any reason you just didn't hardwire a 7 wire connector in ?

In all honesty you'd be best asking the vendor this question.

I have not found a 7-way converter for my car (Nissan Murano 2009), and btw, I live in Europe so ebay/Amazon are usually the cheapest options.
So if I would found a 7-way converter that just plug&play into my car harness, without the need of cutting and/or splicing the car's harness, then yes, I would happily go with such a converter instead of "manufacturing" one by myself.

You might have the wrong converter: https://www.curtmfg.com/masterlibrary/01resources/appguides/Curt_Hitch_App_Guide.pdf

Ypur reference say not to bridge pins #5 an #7: https://en.wikipedia.org/wiki/ISO_s...pin_trailer_connector_Type_12N_.28ISO_1724.29

Yes, the converter might not be exactly what I was looking for but that was the only one I found being compatible with my car (model and year) on Amazon.
Mixing the 58R and 58L pins is considered that a would cause a problem only on "German cars", mine is produced in Japan for US market (althougt I imported and am using in Europe ))
Anyway, even on the PDF guide you mentioned, they provide only 4-way converters so ... yeah, probably not the wrong converter from their spectrum of options but the wrong converter manufacturer

 

As mentioned earlier, does your trailer have electric brakes on it?

 

As mentioned earlier, does your trailer have electric brakes on it?

Well, I don't have a trailer yet but just in case, it might have.

So since I posted my question on the CIRCUITS forum I really want to know if in theory I could build a circuit that will intelligently split the current that comes on a single wire into: the turn signal (with regards that when turning the voltage is intermittent) and separately to brake signal (with regards that when the stop light is ON there is applied a non-intermittent voltage on wire).

The simple solution would be to find a car specific harness for 7-way socket but I haven't found yet, so I have to consider making one.

The harness I bought is a CURT 55571 with T-connector. By looking at that picture (see link) it looks like the CURT converter grabs 4 different signals (green,yellow,red and brown, the white being the earth) from the car harness, but unfortunately it converts them to 3 different output signals (like turn left+stop, turn right+stop, tail/plate/side marker).

I don't really want to cut and slice my car harness so I think that this solution was an elegant one. Besides, the converter does more than that: it protects the car circuit from an accidental trailer short circuit (which is great).

I am not in electronics so the following can be a really stupid idea. Given the fact that the brake and the turn signal share the same wire (and probably the same bulb, behind a red-orange plastic lamp) the problem is how to fork that wire such that:
(1) when the car turn the signal do not light the brake light
(2) when the car brakes do not light the turn signal

Obviously with the aid of an Arduino everything can be done but I am thinking to something much simpler that that, using passive components.

To avoid sending an intermittent voltage to the stop bulb when the car turns the signal (thus sending an intermittent 12V on the common turn-stop wire) I am thinking like using a capacitor and a resistor: the capacitor loads that small qty of energy which is sent intermittently to the stop bulb (which is not desired) and the resistor consumes it. The capacitor must be chose such that if the current flows more than that capacity, the excess will go through resistor to the bulb, thus to the final lamp (see the case of braking). So when the car brakes it sends continuously current to that wire, the capacitor-resistor pair cannot handle it, and let the current flow further, thus to the stop bulb. Obviously in this situation even the turn signal will look like it brakes, but this cannot be avoided without an intelligent chip (or I cannot think to a simple circuit that will know to not send current to the turn wire just because the voltage is non-intermittent). So I think it is possible, I just don't have enough knowledge of how to do it (although I can learn fast, unfortunately I need it in like 1 week so learning how to do it and testing in 1wk is not going to work well).

What do you think?

 

Your description is a bit hard to follow, but what I think you want is:

If the right turn and left turn are activated at the same time -- Activate STOP instead and turn off the "turn signals".

I THINK the idea is that the trailer has independent stop lamps, and independent "park" lamps and independent turn signals.

The stop/park lamp has typically been a dual filament bulb where the low filaments are the parking lights.

 

If you need it in a week get a towbar guy auto electrician to install it.

Thank you for your advice, but I am a little pit-bull. In one week I changed my headlamp entirely, and that was not an easy job (the whole front needed to be dismounted, I needed to make a new harness, etc). So even if that sounds like impossible for someone, I am 100% I am going to fix it. I always do
PS: I know to do exactly the same thing that the most electricians do: cutting and splitting in the original car harness is easy. I try to avoid such a mess, I want a more elegant solution. I already have an elegant plug&play converter (CURT 55571), the only problem is that is grabs 4 different signals (break being a distinct signal as input) and combine them into 3, brake sharing now (as output) the same wire as the turn signal (which sucks!). Otherwise it is a very elegant solution.

I THINK the idea is that the trailer has independent stop lamps, and independent "park" lamps and independent turn signals.
The stop/park lamp has typically been a dual filament bulb where the low filaments are the parking lights.

Yes, that is the main idea with a 7-way socket, isn't it? The left turn signal is independent, the same for the right one, the same for both tail/license-plate lights, one for left and one for right, and obviously for the brake but this is common for both lamps (left/right, but anyway, it is an independent signal).

Yes, probably there is a 2-filament bulb, probably there is a specification for light intensity when comes to stop or turn lights.

Anyway, no one around here have an idea how to make such a circuit so I will start doing tests by myself

I will let you know about the solution I found, who knows, someday someone may need it.

 

Is it just me? I am still not clear on what you want? You want a single filament in a bulb to do two distinct operations? One for brake and one for turn signal?
You do understand how a normal vehicle turn/brake light works? They use the same filament and when the brake is selected, full battery voltage is sent to the filament of the bulb. When turn signals are used, the circuit goes through a flasher unit (bimetal, electronic, solid-state, hybrid) to make and break the circuit (On-Off-On....)
These are separate operations and must remain separate. that is why they make vehicles with a separate turn signal unit from the brake unit. So you can have both at the same time.......on two separate circuits.....using two separate filaments.
If there was a way to help you, there are plenty of people on here far brighter (excuse the pun) that can build anything you want but if I think I understand you, what you want is not possible.

 

em:

Trying to help, but just having trouble following you. The same as BW. It might be part language barrier.

It's a bit of what your car does have an how they operate.

What this box of yours does?

And what you need?

I get the impression that the car has the "right signals", the box "convolutes them" to the wrong signals and you want to make a box that "unconvolutes them" because your uncomfortable with splicing?

We never added the possibility that the cars uses LEDS and does not have the ability to drive the extra lamps.

I thinks that part of the reason 12 V is supplied to the converter.

There are so many ways that brake/park/4-way/markers can exist. In the early days, you used hand signals to turn. Later, 4-way/turn mess was handled in the turn signal switch. In a 2000 vehicle (non-LED) it's handles in the 4-way switch. Finally, you might find each light being independent and controlled via a DATA bus.

You might even find dimming being done by PWM to the same LED bulb. So, it's a real mess out there.

The converters in all likelyness draw only a littlle bit of current (i.e. detect voltage) and drive the lamps from the +12 circuit in the connector, not the car's circuit.

To give you an idea why, if the car had a thermal turn-signal flasher, the flash rate might increase if you added another standard bulb.
If your car has LED bulbs, a real bulb might overload that circuit.

bw is professionally in the automotive business and I'm just somewhat knowledgeable.

 

If there was a way to help you, there are plenty of people on here far brighter (excuse the pun) that can build anything you want but if I think I understand you, what you want is not possible.

Well, if I am going to use the idea of 2-filaments bulb then the CURT converter might fulfill all the necessary functions out of the box, despite having only 3 wires. So if I understood well, it is a combination of converter- 2-filament bulb that makes the solution working (which is smart).

If I am going to use/rent a trailer that has a 7-pin connector, then how should I wire the 4-ways connector of that CURT converter to the 7-way plug on the trailer? Of course, an adapter! But I don't know if an adapter would be able to do that (it could if it behaves like the 2-filament bulb).

I see that you (bwilliams60) have deep knowledge into automotive so perhaps you could tell me what you think about my last statement above.

Would disconnecting the brake signal from the box & running the brake signal straight to your 7 pin connector work ? Seems like a simple solution to separate the signals.

Yes, that sounds plausible. The same way I could disconnect every single wire from the box, actually just dumping the box, and wire the whole thing myself. Is just that I wanted to avoid this.

Left Turn & brake ON = left indicator->flash, right indicator?
Right Turn & brake ON = right indicator->flash, left indicator ?

Are you thinking at a single bulb that is shared for all these functions? If that is the case this would never work (neither on US soil or EU) because you might want to brake and in the same time to turn left, which means:
Left turn & brake on= the brakes lamps should be on, the left turn signal should flash, the right turn signal should be off
Right turn & brake on = the brakes lamps should be on, the right turn signal should flash, the left turn signal should be off

I mean this is the way that a car works, right?

em:

Trying to help, but just having trouble following you. The same as BW. It might be part language barrier.

.

The box hooks into the car harness (both on left and right) by a T-connector to grab the left turn, right turn, tail lamp and brake signals. And the ground, of course. My car has LEDs on the taillight/brakes, but it would make no difference here. Or?

After reading about your 2-filament bulb possibility I don't exclude that the box was conceived for exactly this simple solution: a trailer with a "magic" 2-filament bulb. If that is the case then probably it will send different voltage such that the bulb would be able to execute 4 different combinations:
- both filaments off
- one filament blinking, the other off (the turn signal only)
- one filament off, the other steady light (the brake)
- one filament blinking, the other steady light (brake is applied and the turn signal is ON as well)
So that is the 2-filament bulb approach and that probably works out of the box (I never had chance to test it yet but probably that box works like this).

If I would take into consideration renting a trailer (in Sweden that is as old as the hills) that might have different bulbs (or even LEDs nowadays???) then I should prepare my socket for separate signals (as per ISO 1724). Would a simple 4-way to 7-way adapter do it by itself? It might if it has some hidden electronics there. No idea, though.

THANK YOU all guys, you really help me. The solution might be even simpler than I thought, there is no need to reinvent the wheel after all.

 

@Robert Murphy

Oh man, that is just pure white magic! Finally I am able to see how it works.
Thank you!

 

The dual filament bulb is basically the lower intensity filament is the tail/parking lights. The high intensity is the brake/turn lamp. So, they are a bulb with 3 connections and one common.

If the adapter powers the trailer from the +12 applied to the adapter, +12 is rare in the trunk. In one vehicle, i put a lighter socket in the trunk to charge a laptop. I did that while installing an amplifier.

In a GM vehicle that my family owns (non LED) there is stereo amplifier in the trunk.

The signal to the third brake light could easily become "brake" without any logic.

I've yet to see a schematic with LED turn signals and Brake lights.

The glitch "used to be" is that the 4-way flasher used to flash the ( turn signal lamp which doubled as the brake lamp)