Go to the bulb sockets and trace back the Ground (black?) wire to where it connects to the body. I assume there is a separate one for each bulb, as on '87 I'm familiar with.

Ground on right side is probably a PITA (under washer tank), so work on the LEFT side first. Take the ground wire OFF at body connection and meter the terminal with lights ON -- to see if the 12v is getting all the way thru the socket IN, Filiament, OUT, and thru ground wire.

If 12v is there (at the end of the ground wire), all that's left is the ground connection. Scrape/sand it to bare metal, and reconnect. If it still fails, we need someone smarter.
--
Bruce Young,
940-NA (current)
'80 GLE V8 (Now gone)
'83 Turbo 245
'73 142 (98K)
'71 144 (track modified--and going to be crushed unless...)
New 144 from '67 to '78
Used '62 122 from '63 to '67