Witch wires should have power/ Map switch
I hate this circuit, and since "I don't have one" I really don't have it figured. It's a mess, tied in with the time delay, and the multi-pin door switch on the left side.
You have the 72 shop manual?
In the underdash harness the main harness accessory connector M2 series wire goes up and eventually ties in at the headlight switch terminal of the dome light switch (twist the knob to left) and GROUNDS that yellow
The M6 series yellow goes over and connects to the left side multi terminal door switch, shown in the bottom drawing.
In the top drawing, start at the map light and follow over to the right to B of the time delay, then, M3018P and notice that connects to the "cigar lighter connector" of the main harness THIS IS where 12V hot power is coming in
Then I BELIEVE that the map light switch is a single pole double throw TO GROUND, so the switch I believe must be grounded. I would bet if you unplug the harness from the switch, and check continuity to the switch mounting, one postion of the switch will show continuity to one of the pins, probably the M12BR pin. (brown)
I believe that the M2C wire (yellow) going off is simply tied to the left door switch and turns the lamp one with door open. I could be mistaken.
The PROBLEM is the time delay, as I have no idea what it's internal wiring is or does.