The reason the front bulb is dim then bright in the 2nd vid is because it has two filiments. The dimmer of the two is the parking light fed by the brown wire.
Ok, I hope this helps to explain how they work.
Here is a modified copy of the Autozone wiring diagram.
I simplified it to show only what we are talking about. I also colored the wires to make it a little clearer.
In some ways we are talking about 4 circuits here even though there are only 2 pairs of bulbs and only 3 pairs of filiments.
In the grill we have a single pair of bulbs, but they each have 2 filiments. A dim one for the parking lights and a brighter one for the turn signals.
- The bright side gets power from the fuse box, through the flasher, through the t/s switch in the column and then through the blue wires to the bulb then directly to ground at a point near the bulb on the core support. Pretty straight forward circuit.
- The dim parking light filiment gets it's power from the headllight switch, through the bulkhead connector, down the brown wire to the bulb and then to the same ground as the t/s side. Also (and even more so) very basic.
Then there's the side markers. Here's where it gets a little weird since, as you can see in the diagram they have no visible ground. This is where most people get turned around.
- When the headlights are off and you use the turn signals they are pretty simple. Power comes through the blue wires to the bulbs just like for the front. The ground is actually in the headlight circuit.
- When the headlights are on and the turn signals are off they are also pretty simple. Power from the headlight switch comes down the brown wire to the bulb. But now the current is flowing the other direction and the ground is in the turn signal circuit. (I've heard different oppinions as to exactly where but for this particular problem that's not really important.)
- Now - when you have the headlights and the turn signals on at the same time this is what happens. Like before, the marker light power is coming through the brown wire making that hot rather than a ground. When the flasher sends power through the blue wire that side also becomes hot, interupting the ground on that side. This causes the bulb to go out until the flasher opens and the t/s side becomes the ground again. This makes the bulb flash opposite to the front turn signal.
