Fuzzy & Jay are right. The only way to change the output of a filament is by changing the input power… regardless of wether its a car, bus, house, w/e.
I’m not going to argue about how many filaments you should or shouldn’t have, but if your tailight / brake light is a 1 filament single bulb, then there is a voltage regulator or circuit board involved to make the bulb dim & bright (which is not unpossible)
1156 sockets are single contact / single wire sockets.
http://www.oemsurplus911.com/automotive/lightsockets/8511.htm
1157 sockets are double contact / two wire sockets.
http://www.oemsurplus911.com/automotive/lightsockets/8512.htm
Not surprisingly every parts site & manual calls for a 1157 in your car. You say the sockets have two wires. I’m gonna say that it requires 1157. I’m sorry but until you find pics of both sockets and show me that a 1156 works, I’m going to have to say that you jammed the wrong bulb in there -or- you do not have stock / OEM / correct sockets.
Sylvania themselves say that:
Rear turn signal
1156
1156LL Long Life Upgrade: Up to twice the life of the standard lamp
Tail light
1157
1157LL Long Life Upgrade: Up to twice the life of the standard lamp
Stop light
1157
1157LL Long Life Upgrade: Up to twice the life of the standard lamp
Use this link to see what I mean by non oem socketing. http://www.beyonddarwin.com/Starion/JDMtail.html
I’m going to go out on a limb and guess that since your problematic bulb is staying dimly lit (with parking lights on) and not getting brighter with the brakes applied… you are possibly looking at the wrong socket… but I would’ve thought that you’d notice the appropriate bulb lighting up then… also, this does not explain your other brake light working.
If you want to bring the car here I will take the multimeter to it and see if the voltage changes… thats all I’ve got for you.
Sorry.