I've successfully made a simple Larson Scanner demo from the faceplate module of a Toyota 86120-08010, the stock tape deck audio head unit of a 1998 Toyota Camry LE. It gave me confidence that I wouldn't need the original mainboard anymore.

Nor would I expect to want to probe communication between the original mainboard and the faceplate, both separately and alone. Time for a little cleanup work, undo the tangle of wires and get to something more streamlined.

I started by detaching the wires I attached earlier.

The excellent Engineer SS-02 solder sucker helped me remove all the solder attaching the mainboard connector, freeing it for reuse.

Good news: This connector has two rows of easy-to-solder through-hole pins, with the 0.1" pitch common to perforated prototype boards. The two rows are 0.1" apart as well.

Bad news: The two rows are staggered, which won't fit on a 0.1" perforated prototype board. Reusing this connector properly will mean a custom circuit board.

In the meantime, I can still make use of that connector even if "improperly". I had soldered wires directly to the faceplate for probing and experimentation, but I can move all of those wires to that connector even without a circuit board.

Soldering wires directly to the pins isn't best practice, but it allows me to move and store this assembly with less worry I'll accidentally yank something off the faceplate.