Well, for others, who will want to install a remote something and control it inside the cabin. Here is my story and experience. As Mr Miata offered.
Pull the battery
Pull the battery tray
pull down the carpeting on the passenger side fre wall.
set aside the thick styrofoam insulating block beneath.
Undo the screws holding the underlying panel and (taking care) fold it back out of the way
Reach up and to the right and find the round rubber plug it has one wire passing through it.
This is the plug which will permit passing through the firewall, a wire of considerable size after relieving a suitable size hole in the plug to accommodate it.

Now it is important to note, the panel which is layed over has considerable wiring and parts afixed, so care must be taken, when removing and replacing, so that damage or disturbance to these does not happen. The care taken will be rewarded when stuff still works after the install is complete.

Rusty