Pins 3 and 8 (1 on the right, 9 on the left) on CN8 power the top half of the backbox/speaker panel lights. According to page 26 of the manual (page 31 of the PDF), that is also protected by fuse 2F2.
https://www.ipdb.org/files/2090/Data_East_1988_Secret_Service_Manual.pdf
I'd check that fuse. If it's good, take your multimeter and check for continuity between the connector and the backbox/speaker panel.