Relay circuit for brake/turn signal

Good day folks. I own a Mustang made for Europe. Unfortunately they have modified the tail lights to something I don't like. So as you can see from the photo, the 2 inner strips are red and the outer is amber for turn signal. There is no way to get inside it without cutting the back or cracking the window open. Someone tried the window and it ruined it. I measured some voltages on the wires and I found which is which. I used to think the 2 inner brake strips have two types of LEDs, one for parking lights and one for brake lights, but it might be one that lights more depending on the current. So I'm guessing there is a relay in there that switches between parking and brake lights. Let's go with my guess. The third strip, which is the amber one, has 2 types of LED, one red for parking and one amber for turning. So my plan is to add the outer parking LED to the brake circuit, but also cancel the brake on the outer strip IF the turn signal is on. I'm afraid that if I live it on, the amber will not be visible enough. Besides the fact that I have no idea yet how to modify the wires to add the parking light to brake circuit as I have no control inside, I'm here to ask how to open a circuit using a relay considering the turn signal is 1 and 0, not a constant 1 like brake. When the turn signal is 1, the brake is off no problem, but when it goes into 0, the relay switches back and the brake comes on again. I don't want that. I saw on the website here a circuit using a relay and a capacitor for corner lights. Thing is that capacitor charges slow and also discharges a bit slow. Let's assume my turn signal goes from 1 to 0 in 0.6 seconds and 0 to 1 in the same 0.6 seconds. I need my capacitor to be charged enough to keep the relay in the 87 position when my turn signal is 0 until it becomes 1 again. Thing is a capacitor that charges in 0.6 secs to 6 V for example, discharges in 0.3 secs... according to some circuit simulation websites. I was also thinking of a timer/counter that when it receives signal(the 1 from turn signal) it outputs a constant 1. If it doesn't receive anything for more than 1 second, it switches to 0. All the brake/turn videos I saw have a short delay after the turn is done and the brake applied. If only I could add a FPGA or smth back there to use a simple IF or WHILE... if only... So any solutions for my problem? Thanks a bunch. Regards, Stefan.

I read that I should state details about my car. It's a 2015 Ford Mustang Ecoboost, Europe version. It doesn't have front LED like US does, planning to add those also and the tail lights that I spoke of above.

This guy probably won't be back to see this, but I'll post for future info. The Mustang taillights are CanBus controlled. The intensities are PWM'd. There are no connections to the light modules other than power and data. Not much can be changed without re-programing the module, which one day may be possible. But not at present for the DIY'r.