you have to open the dash, that is, on the side of the instrument cluster you have to take the trim off (and air vent) and reach down. The passenger side you remove the air vent and/or remove the glove box.Since you are on the topic of speakers....
I purchased a set of speakers to replace the 1993 factory speakers and wasn't sure how to access them.
How do you access the 4" speakers inside the lower metal dash panel ?