TOM305T/A

Hello all, my car failed inspection because 3rd brake light not working I don't think it has worked in over 10 yrs. When i check for power on the trunk plate near the pull down I'm suppose to have 12 volts on 1 and 4. i have power just on 1 nothing on the 4. on the hatch where there is suppose to be 2 metal prongs sticking out.that make contact to the trunk connection.on 1 and 4 i only have a prong on 1 and nothing on 4. i guess it broke off at some time. When the brake is depress and hatch closed, i have a black and red wire on the 3rd stop like they both have power. new bulbs, connections look clean. fyi, when i turn defrost the left side has power and the right side does not. if that makes a difference