Finding the read head wiring is easy enough. On my sacrificial hard drive I was lucky enough to have all the connections routed to the back of the drive. Once the circuit board is removed its as easy as following the leads back and then some careful soldering.
One neat little feature my speaker has is the led on the write head. It's also wired into the audio so it blinks quite nicely with the bass.
Zoomed out a bit you can see the cable I used that goes to the back panel. Its a rear panel audio adapter from an old motherboard I had die on me a couple months ago.
I was lucky enough to have an old speaker lying around. it was mostly falling apart so I repurposed the box. (The duct tape is dual purpose, structure, and substitute for new paint)
Around the back you can see the connectors for the audio. The little mic jack there outputs the input from the stereo....which is nice...in case you want to listen through headphones...(for whatever reason)...but the volumes needed to make the head jump and the LED flicker are way higher than headphones (mine anyway) can handle. I learned that the hard way.