Third Brake light does'nt work with Right/Left brake tail-light.

The third brake light comes on when I press the brake pedel with the right and left brake light bulbs are removed. When I replace the bulbs one at a time it doesn't work. I check the fuses and directional light system and they work fine. So check the part number of the dual lamps
and bought new ones, thinking the wrong lamps are in the circuit board.

I check the voltage to the circuit boards without the lamps I measured 12 volts DC but when I install the new lamps into the circuit board I measured less than a volt?

Do I have a problem with the Brake switch under the Brake pedel?

Check the current. n see what you get there.