I had to junk my old car, but I took out the stereo and speakers for this project.
Step 1: Power the Car Stereo
Car stereo needs 12V DC in order to function.You could either use 12V battery or any desktop computer power supply. (In this case, I am using computer power supply)
a. Jump the computer PSU.
b. Find the 12V wire and connect it to the stereo power wire together with ignition wire.
c. Find the ground wire on PSU and connect it to the ground on stereo.
Step 2: Connect Speakers to the Stereo
It turns out the one speaker, that I pulled out of my junk car, was already busted. Therefore, I had to make due with only three speakers.
You will need wiring schematics of your car stereo. Explained in the video.
On the side note. Following could be helpful.
How to check for bad speakers. https://www.instructables.com/id/Easy-way-to-check...
Holes in speaker cone? try this https://www.instructables.com/id/How-to-Repair-Spe...
Step 3: Boombox Design
Video shows the steps to achieve my unorthodox design.
I am not great at wood working. However, I tried my best. Be creative and follow your own design.