issues install flashing module a car 3rd brake light

[SparkyFX]

The output to the third brake light might be PWM controlled anyway.

Yeah it might be, I just don't have a oscilloscope to test it.

Check the voltage with a multimeter while on, it gives you a different mean value when it´s not DC.

[wojtek077]

My suggestion was to draw around 25W on the brake light circuit to force the voltage when off to drop to zero.  i.e. put a 6ohm resistor in parallel with the entire thing.   

If the existing one is only drawing 1W this would be too much.   

You could also try a 3.3V zener backwards so that it adds 3.3V of drop.

Sorry late reply but what zener would use I'm getting overwhelmed with data sheets and how would wire it up towards the ground or positive side.

Edit/Addition:   It also occured to me just after I posted this reply that there are circuits out there which will cut off below a certain voltage.  Usually they're used to prevent overdischarging a rechargeable battery or prevent something from running at too low of a voltage.   If you google 'low voltage cut off circuit' or 'low voltage disconnect circuit' you'll probably find a few.   

I been looking but I couldn't find one. I found relay ones but I don't trust those. I wonder if there will be a delay with the zener?

[wojtek077]

Something like this

[forrestc]

See section 3 about a voltage shifter at this page:

https://circuitdigest.com/tutorial/zener-diode-types-applications-and-operational-principle

The resistor probably isn't needed in your application since your device will stand in as the resistor.

You choose the zener based on the amount of voltage drop you need.  You'll also need to size it big enough current-wise and power-rating wise so that the amount of current you're passing through the zener doesn't result in the zener overheating.

[ledtester]

fwiw, here is, I believe, the first patent granted for a flashing brake light: #3,460,089 granted in 1969:

https://patentimages.storage.googleapis.com/62/e6/3a/432bbdfbb55446/US3460089.pdf

It is interesting to read how it works. No 555 timers or even any solid state electronics here:

When wire 12 warms, it expands permitting bus bar 5 to shift to the left under
the expansive force of leaf spring 16 against stop 17, causing contact 6 to open.
Without current coursing through it, wire 12 cools, contracts and closes contact 6
once more. In that manner the cycle is repeated. The frequency of the cycle can
be adjusted by varying the value of the resistance in wires 11, 12, 13, the thickness
of leaf spring 16, and the deformation of leaf spring 6 from its unstrained configuration.

[james_s]

That sounds an awful lot like the ordinary thermal flashers that have been around for decades. It wasn't until the 80s that I started seeing electronic flashers used for turn signals.

I remember you could get thermal button flashers that stick on the end of a lightbulb base. They worked well at first but eventually the bulb would heat up and the flashing would get feeble, only blinking off very briefly.

[wojtek077]

See section 3 about a voltage shifter at this page:

https://circuitdigest.com/tutorial/zener-diode-types-applications-and-operational-principle

The resistor probably isn't needed in your application since your device will stand in as the resistor.

You choose the zener based on the amount of voltage drop you need.  You'll also need to size it big enough current-wise and power-rating wise so that the amount of current you're passing through the zener doesn't result in the zener overheating.

On voltage fine but when I release brake pedal there's still leakage. Can I put the zener backwards and do a low voltage cut off?

[wojtek077]

fwiw, here is, I believe, the first patent granted for a flashing brake light: #3,460,089 granted in 1969:

https://patentimages.storage.googleapis.com/62/e6/3a/432bbdfbb55446/US3460089.pdf

It is interesting to read how it works. No 555 timers or even any solid state electronics here:

Wow 1969

[james_s]

I'm not sure why that is surprising, turn signals had thermal flashers at least as far back as the 1930s. By 1969 solid state flashers were possible, I mean we had computers, transistor radios, jet airliners and moon rockets by then.