Tail lights not working after changing drivers side light un

I had reason to change the rear driver's side light unit on my 1996 S40. When I swapped the unit with one from fleabay I discovered that all the lights worked except both tail lights and one tail light on the other passenger side unit which seemed to fail in sympathy. On closer inspection there is a light control module fixed to the light unit in the driver side light which I think selects the inner tail light bulbs on with the ignition on only. Although I then swapped this module from the old light I only managed to get the outer tail lights to work. The inner tail lights on passenger and drivers side refuse to work. Bulbs are Ok and fuse is OK. I'm now looking at having to buy this light module thingy believing I've managed to fry it somehow. Does anyone know what's going on with control of the rear tail lights here? I wouldn't be too bothered but the MoT tester is adamant that all 4 tail lights must work. Thanks for any help.

Sorry to ask this but is your ignition on? Inners only work when it is.

sorry for the stupid question but have you checked the fuses..........if you have tow bar you may find moving the lamps the live may have earthed out........only saying as i did it at work on a transit van........

Yeah - I have seen my wife driving off several times and noticed the sequence of events for the tail lights (exciting life some of us lead). I have tried light switch on only which puts outer tail lights on following by ignition which should turn on inner lights as well. Currently the inner lights don't work with ignition on or off. Just as an experiment I unplugged this light control module thing at the bottom of the drivers side tail light and it makes no difference to the lights - the outers continue to work, that's why I suspect this module is at fault. Only Volvo can make something unecessarily complicated although to be fair it has worked for 248k miles until I medalled with it!

If you mean the black box with the white multi-plug, I have just been out and tried disconnecting mine, inner lights came on when connected and disconnected.

Might be getting somewhere with this - the module in the RH brake light is the brake failure warning unit, so nothing to do with the tail lights. The local Volvo specialist says the tail light holders aren't the best and slight knocks etc can put the bulbs out/blow them regularly. Come to think of it can't remember the last S40 saw with all 4 working! I'm going to recheck everything and will report back.

OK - fixed this now, the inner tail bulbs had coincidentally decided to fail (very black glass but filament looked ok). Replaced all bulbs and everything working again. Adjusted bottom bulb contact in holders as these seem to make intermittent contact otherwise.