Originally Posted by onehundred80
I'll take one more stab at this, the picture shown on ebay has two terminals that are for two circuits in the bulb, I'd guess two sides for rear light and four sides for rear and brake lights. Does your bulb have two terminals? I am surprised that a single filament bulb even lit up, as they have a center terminal I thought. A single filament would not get any brighter, as 12 volts is still 12 volts even if the center terminal touched both contacts. For the same reason I cannot see the third brake light getting brighter.
I would suggest putting the correct bulbs in and see what happens, this would show if there is a problem with the circuit and lay the cause of the problem on the LED's if there is no problem.
I currently have the old filament bulbs back in and everything is operating exactly how it should. The base of both the filament bulbs and the LED bulbs look the same, as you said two terminals (metal pieces) on the bottom of each bulb. With that info, would you say a resistor is the right fix? To trick the car into thinking the bulbs are getting the same amount of resistance as the filament bulb does anyone know what resistor would be necessary to splice in?