So I was looking for the gas door release button on my new '85 GS, and I can't find it. I found what looks like the guts of a momentary switch below and to the left of the steering wheel, which I am assuming is where the button should be. My question is this: How can I release my gas filler cover with the push button missing?

 

When I bought my car the button was broken, and the guy carried a butter knife in his storage bin for opening it. I guess he jimmied it around in there some how.

Than I got a new switch off a parts car, and wired it up.

 

looking at the FSM there should be a T connector with two wires, one Blue-Red and the other Green-Black. If you close the circuit by connecting those two wires it should open the gas door.
There is also a fuse to check if it doesn't work.

That's what I understood from the FSM. Correct me if I'm wrong.

 

You can reach in between the upright carpet finisher in the hatch and the interior plastic wheel well cover. Feel around for the lever and pull back. If you want to repace it, you can either find a used release button/solenoid from another forum member or replace the fuel door with one of the keyed locking ones.

 

Once you locate the lever on the release solenoid, you could attach a cable to it, and just release it from inside the hatch. I dunno why Mazda didn't place an emergency release cable on these, I guess they didn't expect the switch or solenoid to ever fail...
Later models got the release cable, though.
As for replacing the door with one that uses a key, just remember that anything that will go into the "lock" will release it. It's not a real lock.