How to wire audio in truck

So I bought a 1991 b2600 in almost perfect condition. 116k miles) But one problem is that the audio doesnt work. iIcan tell it has been tampered with - there are what seem to be speaker housings under the dashboard but with no speakers. It had some old kenwood radio that I took out today. wow so many wires behind it. So my question is where are the speakers located in the car? and what color are the wires connected to them. pictures would be nice) i have a feeling that I'll have to take out the whole side panel.. Yeash Also any advice on rewiring and putting new speakers and radio? Totally thankful for any info

Welcome. I've had my '88 B2200 for 21 years now. The underdash speakers are 4 inch size, I use that location still. Unless someone has wired up/installed speakers in the door, I'd keep the stock location.

On mine, back in 1994 I installed a new stereo (cassette stereo). If - big if - if the original Mazda wiring harness(es) are still there, I'd buy on Internet/purchase a wiring adapter kit. On mine, I just soldered-in new wires in parallel (without cutting original wires) so I would retain the original capability. If a previous installer just cut those away, you can use the factory wire colors or the Kenwood wiring colors to figure out which wire is what. For example, on modern stereos yellow is typically "always powered 12 volt positive" for the memory/clock and red is "ignition switched 12 volt positive". I suggest soldering for wire connections instead of crimp connectors.

Here's the general Mazda color code for stereo; very few trucks actually had rear speakers from factory (Cab Plus LX models). You'll likely need to run a separate ground wire to chassis metal, like around a mounting screw.
Battery 12 volt positive always

Wow thanks for all the info! that really cleared things up. So what you are saying is that i only have to put in front speakers? I suspect that there arent any back speakers in the housings. So untill I have more dough and time I'll just work on the front ones. they are waay easier to access anyway

Most of us are fine with just front speakers.

Yes, to put speakers into the housings in the rear of a Cab Plus is difficult, see