What size speakers do I get to fit a 1990 Nissan

What fits you car is on the white label inside the door
on the A or B pillar.

A tire store will have a listing also

2002 Nissan Sentra Car Stereo Radio Wiring Diagram

Car Radio Constant 12v+ Wire: Pink
Car Radio Switched 12v+ Wire: Blue
Car Radio Ground Wire: Chassis
Car Radio Illumination Wire: Red/Green
Car Stereo Dimmer Wire: Red/Yellow
Car Stereo Antenna Trigger: N/A
Car Stereo Amp Trigger Wire: N/A
Car Stereo Amplifier Location: N/A
Front Speakers Size: N/A
Front Speakers Location: N/A
Left Front Speaker Positive Wire (+): Pink
Left Front Speaker Negative Wire (-): Blue
Right Front Speaker Positive Wire (+): White
Right Front Speaker Negative Wire (-): Black
Rear Speakers Size: N/A
Rear Speakers Location: N/A
Left Rear Speaker Positive Wire (+): Light Green
Left Rear Speaker Negative Wire (-): Violet
Right Rear Speaker Positive Wire (+): Blue
Right Rear Speaker Negative Wire (-): Pink

1990 Nissan/Datsun Sentra 1.6L FI SOHC 4cyl the Flasher is located front seating area, driver side, under dash, driver side of brake pedal, mounted on support bracket.

Hope helps.

2002 Nissan Sentra Car Stereo Radio Wiring Diagram
Car Radio Constant 12v+ Wire: Pink
Car Radio Switched 12v+ Wire: Blue
Car Radio Ground Wire: Chassis
Car Radio Illumination Wire: Red/Green
Car Stereo Dimmer Wire: Red/Yellow
Car Stereo Antenna Trigger: N/A
Car Stereo Amp Trigger Wire: N/A
Car Stereo Amplifier Location: N/A
Front Speakers Size: N/A
Front Speakers Location: N/A
Left Front Speaker Positive Wire (+): Pink
Left Front Speaker Negative Wire (-): Blue
Right Front Speaker Positive Wire (+): White
Right Front Speaker Negative Wire (-): Black
Rear Speakers Size: N/A
Rear Speakers Location: N/A
Left Rear Speaker Positive Wire (+): Light Green
Left Rear Speaker Negative Wire (-): Violet
Right Rear Speaker Positive Wire (+): Blue
Right Rear Speaker Negative Wire (-): Pink

1990 Ford Thunderbird Car Stereo Wiring Diagram
Car Radio Battery Constant 12v+ Wire: Green/Yellow
Car Radio Accessory Switched 12v+ Wire: Yellow/Black
Car Radio Ground Wire: Black/Light Green
Car Radio Illumination Wire: Blue/Red
Car Stereo Dimmer Wire: N/A
Car Stereo Antenna Trigger Wire: Orange/Blue
Car Stereo Amp Trigger Wire: N/A
Car Stereo Amplifier Location: N/A
Car Audio Front Speakers Size: 5′ x 7′
Car Audio Front Speakers Location: Doors
Left Front Speaker Positive Wire (+): Orange/Green
Left Front Speaker Negative Wire (-): Black/White
Right Front Speaker Positive Wire (+): White/Green
Right Front Speaker Negative Wire (-): Black/White
Car Audio Rear Speakers Size: 5′ x 7′
Car Audio Rear Speakers Location: Side Panels
Left Rear Speaker Positive Wire (+): Pink/Green
Left Rear Speaker Negative Wire (-): Pink/Blue
Right Rear Speaker Positive Wire (+): Pink/Blue
Right Rear Speaker Negative Wire (-): Green/Orange

Try crutchfield web site.when i was replacing the ones in my truck they had notes on the ones that were direct fit and ones that you would have to modify the hole or stock grill. well hope this will help you out.

if you are putting an after marker stereo the wiring is different from a stock radio some audio stores sell adapters for after market stereos that you jus clip on to stock wiring

The size of speaker that will go into that vehicle is a 6 1/2". You will need to take off the door panel in order to remove speakers. Once door panel is removed, locate screws holding speakers and remove and reinstall new speakers.

1995 Nissan Sentra Car Stereo Radio Wiring Diagram
Car Radio Constant 12v+ Wire: Pink
Car Radio Switched 12v+ Wire: Blue
Car Radio Ground Wire: Chassis
Car Radio Illumination Wire: Red/Blue
Car Stereo Dimmer Wire: Red/Yellow
Car Stereo Antenna Trigger: N/A
Car Stereo Amp Trigger Wire: N/A
Car Stereo Amplifier Location: N/A
Front Speakers Size: N/A
Front Speakers Location: N/A
Left Front Speaker Positive Wire (+): Pink
Left Front Speaker Negative Wire (-): Blue
Right Front Speaker Positive Wire (+): White
Right Front Speaker Negative Wire (-): Black
Rear Speakers Size: N/A
Rear Speakers Location: N/A
Left Rear Speaker Positive Wire (+): Light Green
Left Rear Speaker Negative Wire (-): Violet
Right Rear Speaker Positive Wire (+): Blue
Right Rear Speaker Negative Wire (-): Pink

theres a small panel behind the door lock and handle.
pop that off, and unscrew the screw found.
After that, it just pops off, and back on.
You have to disconnect all the wires, of course.

I had to pop them off to tint my windows.