The joystick

The joystick goes in port 1

Most C64 games read the joystick in control port 2, which the keyboard does not share. Ghostbusters reads port 1 and nothing else, as its manual says.¹

Port 1 shares its register with the keyboard's columns ($DC01), so a joystick move and a key press can be mistaken for each other. The game's own keyboard scan guards against that: it gives up while either port reads anything but "nothing pressed" ($96CA, $96E8), so pushing the stick never types a key.

The keys

Function keys to start, and space for a report

The keyboard starts the game, types the name and the account number, and in play gives a status report and a pause.

Control	Where	What it does
F1 on the title	$6399	the interview
F3 on the title	$63A8	with a name typed since power-on, straight to the vehicle page with the stored account; otherwise as F1
Space on the title	$6385	"Ghostbusters!"
Space in play	$7175	BACKPACK POWER AT XX% OF MAXIMUM... X EMPTY TRAPS... X MEN LEFT on the ticker
RUN/STOP	$70BA	pause, only on the map, the drive, a bust, and Zuul's street
RUN/STOP and RESTORE	$6425	back to the title
B on the map	$7F70	a dollop of bait
1-3, E in the shop	$7A5B	pages; E leaves, once a trap is bought

F3 is a shortcut for the next game. The flag that says a name has been typed ($6328) survives RUN/STOP and RESTORE and the cold start at the end of a game, so F3 skips the interview and starts with the account the last game printed.