It turns on when you put it in reverse.... well... i put a yard passenger side tail light(replaced my lenseless passenger tail light)... the reverse light worked before with my original ones... when i put the other one in, the reverse light won't turn on, but everything else light up... the brake lights and the signal lights... my reverse light on the driver side tail light worked before, but now it doesn't...

Is it due to a burnt bulb on the right side and causing the circuit for both to fail??? or is it something else???

 

well, simple things first: check the bulbs and the fuse.
If that doesn't help you, check grounds. Then cry for help

 

check the connection in the globe holder, the getting old so there all starting to get a little corosion on em now.. if the contact looks greeny white then give it a good scrape to bring back the metal so it will make contact.

 

you need to make sure the bulb plugs aren't mix up. and put the right bulb in the right sockets.