Odd amber turn signal/parking bulb question.

[Turbo6Smackdown]

My amber turn signal/parking bulbs (in the little lights in the front bumper) are dual filament. Anyone know why? When I turn the lights on and attempt to put the bulbs in backwards (you can't because the nubs are offset to prevent this) both filaments light up, but when it's in the correct way, only one lights up, and it's dim at that. (which seems perfectly normal to me. the lights light up perfect like that)
Why is this?

 

[Topjimmy]

One filament is for the running light, the other for the turn signal.

 

[pacecarta]

if its dim you have a ground issue on the socket or at the fender , its very common for the socket to have issue with ground due to corrosion

 

[Turbo6Smackdown]

One filament is for the running light, the other for the turn signal.

There has to be a totally separate filament just to blink? Why couldn't the blinker just blink the main filiament?

And no dimness issues, because after changing out the lenses for brand new ones, and replacing the 194 bulb on the passenger side, they've never shined so bright. They are fantastic now. I love it. Any brighter than this and I think they'd be kinda silly. I think I'm where I'm supposed to be at with these.