I, along most of the free world, have a cell phone. Using the cigarette lighter port in the Miata to power it has has a couple of drawbacks.
1) It only is active when the ignition is on. This means that charging the phone at night in the car means having to leave the key in the accessory position, and remembering to turn the radio off, etc., to prevent a completely dead battery in the morning.
2) The power cord runs across the shifter, and really looks untidy. I hate untidy.
My solution was to install a permanently hot power port wired straight from the battery. Behind the passenger seat, next to the ECU is a nice empty spot. The carpet is conveniently raised here for the ABS computer, that my car does not have.
21st century America Lawsuit warning: I am not a qualified automotive technician, nor an electrician. (although I play one on the web) Wiring things incorrectly can/will destroy you, your car, or the electronics contained therein. If you attempt what I am describing here, and you kill yourself, blow up your car, fry your ECU, deplete the ozone, cause a cattle stampede in Wyoming, it's not my fault. None of it. You've been warned.
I ran 14 gauge multi strand wire (Purchased at Radio Shack) from the battery, through the tunnel behind the passenger seat. I used an inline 10 amp fuse to protect the wiring, and ran it into a dual power port purchased from Pep Boys. You only need to run a hot lead, there are several bolts in this area to ground to.
The phone adaptor plugs into the power port, the carpet lays on top of the whole thing, keeping it tidy. The phone itself fits very nicely between the passenger seat and the shift console, and the wire runs down between the seat as well, staying pleasantly out of sight.
I now have 24/7 power to my cell phone. (Which, by the way is absolutely impossible to use while driving a top down manual shift car but is handy when, you get where you are going and need to call/be called.)
The dual port also powers my lap top computer which runs the GPS.
Total cost approx $15.00. Total time < 1 hour.