98 bravada speakers

I have a 98 old's bravada and only my driver's side speaker works. The other three don't. I have other problems I'd rather fix first but when I get to this where would be the best place to start?

See if its getting voltage at the speaker. If so, its the speaker. If not, its in the line, or radio. Get a schematic of the wiring at the radio, deterine which wire feeds to the problem speaker, check for volts. Thats how I would do it. Not sure if there is a speaker tech here.

If no volts at the very back of radio, then there is your problem.