I guess the only way to find out if things are switched around back there is to remove the instrument cluster and check the clors of the wires against the wiring schematic.
Or maybe there is a harness connector you can test/troubleshoot back up to the bulbs. I have a nice inductive tone sensor (used for telephone repair) that works great for stuff like this. Owning several British roadsters in the 80s made it a must to have.
'84 190E 2.3
'83 Porsche 944 (track car)
'84 Porsche 944 (parts car)
85.5 Porsche 944 (sled)