Go into switch test mode.
When you see the number 15 flashing on the displays to indicate the tilt switch is closed, pull the J2 connector (playfield switch wiring harness) off the MPU board live.
Do the same again by pulling the J3 connector (cabinet switch wiring harness) off the MPU board live.
Depending which connector stops the switch closure will tell you if it's the playfield tilt or cabinet tilt to concentrate on.