You can test the switch out of the car per this info, and use it to know when/what should be connected.
B1 (Battery 1) should connect to H (Headlights) when the switch is pulled all the way out. There is an internal circuit breaker between these 2 contacts; those can fail open occasionally.
B2 (Battery 2) should connect to R (Rear? Red? the tailights anyway) and to P (front Parking lights) when the knob is pulled to either the 1st or second positions.
B2 also feeds the dimmer rheostat in the switch; the resistance from B2 to I (Instrument lights) will vary from maybe 15-20 ohms down to near 0 ohms as you rotate the knob.
D (Dome) should connect to the switch's metal case/body when the knob is turned all the way to where it 'clicks' to turn on the dome light