there is infact a harness kit for the 1g and a dash kit too.
Mazda In-dash Receiver Kit Fits select 1986-up models Chassis sizes S & E, rack-mount at Crutchfield.com
Receiver Wire Harness For select Ford, Kia, Mazda, and Mercury models, 1983-up at Crutchfield.com
and if your the only 1g member left with a working antenna
Mazda Power Antenna Relay 1979-up at Crutchfield.com
Mazda In-dash Receiver Kit Fits select 1986-up models Chassis sizes S & E, rack-mount at Crutchfield.com
Receiver Wire Harness For select Ford, Kia, Mazda, and Mercury models, 1983-up at Crutchfield.com
and if your the only 1g member left with a working antenna
Mazda Power Antenna Relay 1979-up at Crutchfield.com