How do you replace rear speakers on 1990 Toyota 4runner?

Remove the rear interior panel. It will simply pull away with a little force.

You will need to remove the Philips screw on the rear seat catch and the bolt on the rear seat belt first. It is also a good idea to remove the molding under the tailgate.

The speaker will be located behind the built in grill. FYI, Toyota uses a power speaker with built in amplifier. Best to replace with same.