1955 ford thunderbird

remove the back seat reach in with something and finagle the mechanism , or pick the lock , I've opened locks with keys from other cars of the same brand

If I read the question correctly, he's asking how to open the trunk from inside: he's inside the trunk..... If I'm correct, you don't use a key inside the trunk; you just trip the trunk latch; might be difficult to do in the dark.

Question: If the spare's still in there, how did you fit inside the trunk? I'd really like to know.

A locksmith. Jim