[SportTuner.com]

Most of the 1st Gens require the dash to be cut if it has the original P chassis or corporate unit in the dash. Some of the later years like 84-85 will allow you to slightly trim the radio hole and mount a standard Din sleeve.

Due to the age of the car and possibility that it maybe factor amplified it is generally best to go ahead and run new wires for speakers. I thinks some of the very early models used common ground speakers which will not work with today’s modern headunits.

Here is what I have in my notes on the 1st Gen radio stuff, hopefully it will help answer some questions.

1979-83 Mazda RX7 Car Audio Wiring Guide

Car Radio Battery Constant 12v+ Wire: Blue/Red
Car Radio Accessory Switched 12v+ Wire: Red/Black
Car Radio Ground Wire: Chassis
Car Radio Illumination Wire: Blue/White
Car Stereo Dimmer Wire: N/A
Car Stereo Antenna Trigger Wire: N/A
Car Stereo Amp Trigger Wire: N/A
Car Stereo Amplifier Location: N/A

Car Audio Front Speakers Size: 4″ depth 2.3”
Car Audio Front Speakers Location: Kick Panels

Left Front Speaker Positive Wire (+): Blue/Red
Left Front Speaker Negative Wire (-): Blue/Yellow
Right Front Speaker Positive Wire (+): Blue
Right Front Speaker Negative Wire (-): Blue/White

Car Audio Rear Speakers Size: 6 1/2″ depth 3”
Car Audio Rear Speakers Location: Side Panels

Left Rear Speaker Positive Wire (+): Blue/Red
Left Rear Speaker Negative Wire (-): Blue/Green
Right Rear Speaker Positive Wire (+): Blue/White
Right Rear Speaker Negative Wire (-): Blue/Green

Metra Kit’s available for easier installation:
98-7599 Pocket Kit
99-7500 Multi Dash Kit
99-7501 Multi Dash Kit
70-1781 Wire Harness
71-1781 Wire Harness Auto Side

That what it should be. However if someone’s changed stuff it may nolonger be correct.

Hope that helps you out some. If you need further info don’t hesitate to ask.