Umm yeah, the MPU board connectors have pin 1 on top counting down, meanwhile the main lamp board connectors have pin 1 on the bottom counting up :-/
Actually, the Aux lamp board also has pin 1 on the bottom of the connectors counting up.
We might as well try the tests with your red multi-meter and see if it produces anything meaningful.
Set your multi-meter to read DC voltage on the 20 volt scale (i.e. point the meter dial to the "20" position which on a dial clock would be between 10 and 11).
Connect the black meter lead to ground - you can use test point 2 "TP2" on the lamp board which is ground and keep it connected there for all the below tests.
Connect the red meter lead at the following points one at a time and record/report the voltage measurements:
a1) Main lamp board U1 pin 1 (left most bottom pin of U1)
a2) Main lamp board J4 pin 13 (13th pin from bottom of J4)
b1) Aux lamp board J1 pin 3 (3rd pin from bottom of J1)
b2) Aux lamp board U1 pin 11 (very middle pin along the left side of U1)
c1) MPU board J1 pin 11 (11th pin from top of J1)
c2) MPU board J1 pin 8 (8th pin from top of J1)
d1) MPU board U10 pin 19 (second right pin on the bottom of U10)
d2) MPU board U11 pin 39 (second left pin on the top of U11)