I want to wire up something in the trunk and I need to figure out how do I get a wire from the trunk of the convertible into the main cabin.

 

Coincidentally I'm trying to figure out the same thing...I want to run a video cable for a rear view camera which I would attach to my camper. The wireless cameras just don't have the range.

I'm fairly certain the back seat has to come out but not sure how hard it will be to fish wire after that.

 

Oh no...in that case I might just run the wire externally.

I'm just trying to install a rear fog lamp by drilling out the OEM taillamp assembly. I don't feel like taking out the rear seat...

 

Removing the rear seat is not that hard. There is a fuse panel in the trunk on the driver's side that has fuses for the convertible top, so there is a wire harness going through the metal that you could run your wire along side.

 

There are large holes through the rear bulkhead on both sides of the car where OEM wiring goes to the trunk, but you will have to at least partially remove the rear seat to access them. It isn't hard, pull the rear cushion up, take out a couple of small bolts, then pull the seat back up to give access to the holes. There is plenty of room on either side of the car to run whatever wiring you want to add along with the OEM wiring. This is the left side of the car, there is a similar hole in the bulkhead on the right side of the car:

 

I just ran mine...DennisMik and WylieKylie are spot on. Only tool needed is a deep 12mm socket. Fairly easy on the convertible as you can put the top down and have plenty of room to remove the back seat. Then put the top up to run the wire.
Here are some pics in case you decide to try it:

Lift up on each rear seat cushion-no bolts, just hooked in. Back of seat has two 12mm bolts on each side as shown.



Seat cushions are held down with these steel hooks. They take a fair amount of jerking to get them loose. I broke one of the plastic receivers somehow but ordered a replacement. I suspect you should start from the inner most first.



Top of rear seat on each side has plastic cover that is held down with 3 plastic tabs. There are 12mm nut/washers--careful not to drop or loose these.



Rear seat also has steel hook in center which has a landing spot shown here.



Here's the opening on the drivers side I used for wires.



Here's a view from the trunk. Note the convertible top fuse panel on the left--you could route wires there. (I have a piece of velcro around mine as I'm currently tapping power for another need.)



A closeup of the wires going through. I fished extra wires for potential future needs so I only have to do this once. I've coiled them up and left them under the seat cushion.

Hope this helps.