any one know

[6771plymouth]

passenger side trunk what goes in this hole

[MEK-Dangerfield]

You don't mention what car or what year.

I'll assume it's a Challenger, and guess it's a hole for some kind of recovery system for the fuel vapors in the fill tube.

If you have a Cuda, then I truly don't even have a guess.   

[anlauto]

1970-72 Fuel tank vent tube. 70 is different than 71-72 but both Cudas and Challengers had them

[anlauto]

1971 Challenger

[dfrazz]

It is the hole for your vent tube from the fuel tank.  I'm not sure about Cuda's, but '71 Challengers (and later I believe) required these for pollution control.  There were 4 vent lines mounted inside the vent tube down inside the passenger rear quarter with one or two coming from the fuel tank.  I recently replaced my trunk floor with one from AMD and pulled the vent tube and lines out since the new floor did not have this hole.  I am also running a sending and return fuel line.

[dfrazz]

Also that vent tube is capped at the top and does not go anywhere.

[6771plymouth]

sry its a 71 cuda,  thank you.. kind of wish I dismantled the car so I know were things go but I bought it in this state so its gona be a long project... 

[CudamanTom]

sry its a 71 cuda,  thank you.. kind of wish I dismantled the car so I know were things go but I bought it in this state so its gona be a long project... 

I'm in the same boat with my vert. Luckily I have a hardtop to refer to on most stuff. Both are projects though.
Bought them both stripped down and some stuff I'm learning what goes where.
I'm so lucky to be a memeber on this forum. If these guys on here don't have an answer, then there isn't an answer to be had.