Third break light doubled as a parking light

Thread Starter

Ping pong

Joined Feb 13, 2022
34
I plan on making the third break light on my car also run as a parking light. From factory, the third break light turns on when I break and stays off otherwise, not getting any power when parking lights are on.

Since the third break light is brighter than the regular rear parking lights/tail lights, I will be using a pwm dimmer to dim the break light when it is being powered by the wire coming from the parking lights. The dimmer I will be using is as follows:

https://a.aliexpress.com/_mtkHEPI

The problem is, I don't understand how I will be wiring all of this together.

I understand i might need a relay to switch power between the two wires (break and parking/running) but how will it fit in the circuit, I'm still trying to figure out.

I want to retain the function of the third break light while also making it run as a parking light at a lower brightness. So when I break, the lights blast at full brightness but when it is getting power from the parking lights, it will run at a lower brightness.

The third break light that I'm trying to fiddle with doesn't draw any more than 1amp.

P.s. I am a commerce student and am still new to the whole electrical stuff :)
 

Ya’akov

Joined Jan 27, 2019
6,857
Welcome to AAC.

Though I can't find specific information about the regulations in Pakistan, in many other places what you propose would be a violation of regulations governing the lighting permitted on a car. I would strongly encourage you (if you haven't already) to research this topic and make sure you are not in contravention of local law before actually doing it.

A general hint concerning the implementation of your idea is that you can probably do current steering with diodes to avoid relays. To get a good answer you will need to provide a schematic or wiring diagram for your particular car, or failing that, at least the make and model.

The theoretical version of the solution is simple but the practical version will be heavily influenced by the wiring in the car.
 

Thread Starter

Ping pong

Joined Feb 13, 2022
34
The wiring diagram is attached below. The car is Toyota Corolla 2010. As far as I know, using the third break light as a running light wouldn't go against the local laws, however, I'll definitely look into it a bit more before working on this mod.

I do already have a few spdt relays with me hence why I planned on using those for this project. I didn't understand what you meant by current steering (again, pretty noob at this kind of stuff). Basically I want the effect as explained in the following video (skip to 2:30):

But since they don't ship their products to my country, I planned on doing it myself as I think I can make it work at a much lower cost.
 

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Ya’akov

Joined Jan 27, 2019
6,857
The wiring diagram is attached below.
Unfortunately, even a thorough search of the diagram fails to turn up any mention of brake lights at all. Do you have a page number where you've found the connections?

Since the diagram appears exhaustive, the lack of turn signal and brake light connections is confusing. Is there a separate document for indicator wiring?
 

Ya’akov

Joined Jan 27, 2019
6,857
For someone else who might want to help, here is at least the center brake light connection. I recall how much I dislike car wiring diagrams while looking for the parking lights. I have to get moving on the day but I will try to return to this. With any luck, someone will find this interesting and jump in before I get back.

Sorry I had to bail for the moment.

1668421140002.png

 

Thread Starter

Ping pong

Joined Feb 13, 2022
34
Figured it out! I had done this on a small project previously as well where I gave power to a set of LEDs on my car from two different sources. This is basically the same thing just with a dimmer in between. I used two 1A diodes previously (don't remember their name but I have a few of those with me still).

I made a small diagram quickly to explain how the circuit will work. Pease do ignore my incompetence in making diagrams with correct symbols, I'm still an amateur at this stuff XD
 

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Ya’akov

Joined Jan 27, 2019
6,857
Figured it out! I had done this on a small project previously as well where I gave power to a set of LEDs on my car from two different sources. This is basically the same thing just with a dimmer in between. I used two 1A diodes previously (don't remember their name but I have a few of those with me still).

I made a small diagram quickly to explain how the circuit will work. Pease do ignore my incompetence in making diagrams with correct symbols, I'm still an amateur at this stuff XD
This is the current steering with diodes I mentioned at the start. I‘m glad you worked it out. From what I could glean from the wiring diagrams, the power to the light isn’t mediated by anything between the brake pedal switch and the light itself so there should be no problem with this approach.
 
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