the Sega Model 2 boardset has multiple pieces to the audio puzzle. I'd grab you a picture of the wiring connections, but our *dead* Top Skater's kinda buried in a storage room, and I have a LOT of work to get done today.
open the metal cover behind the TV unit. yours might be held in by screws or maybe you'll be lucky and have the correct key to open it.
try to follow here...
there's going to be the large caged in unit, that's the main board stack (it's really a series of boards interlocked if you didn't know) ... outside of it will be a filter board with connectors plugged into it. there will be separate cabling for the sounds and the music, the sound one will have like a red and black criss-cross pattern on the outside of it.... the music one if I recall will be kind of like this, but a little wider connector.
those run to the sound board, you'll spot this by being a small board with ROM chips in it and it will have red and white (or maybe it was red and black?) RCA jacks on it, kinda like what you hook up to your TV.
those RCA jacks then feed out to another board, which is the amplifier, which of course then goes to your game speakers.
your mission? find the disconnected music cable and reconnect it.
all the connections that go to the filter board on the cage are different lengths and you really can't plug them into a wrong spot. try to get pictures if you need additional help... I'm just going based on memory with the Daytona USAs I've been fucking with for many years now. those have worked fine as of late... knock on wood.
all the unusual wiring harnesses you find in the coin door are more than likely interfaces and power connectors for a bill validator unit. nothing to worry about. I found a lot of the same stuff in our House of the Dead.
good luck.