I've had a slightly odd problem come up with the rear lights on my 156 (2.0TS 2001).
The n/s rear light & brakelight failed the other day, so I replaced the bulb assuming it had just blown, but it still doen't work properly.
Now, when you switch the lights on, they all come on okay other than the n/s rear. If you put you foot on the brake however, the n/s brake light and rear tail light come on, and when you take your foot off the brake the tail light stays on. If you switch off and start again, it's the same - no tail light until the brake light comes on. The other odd thing is that when you turn the lights on first, the tail lamp glows very faintly ( you can only see it with the cluster out - a faint orange glow on the filament) The o/s tail light doesn't do this, so it obviously some sort of fault.
I've taken the rear cluster out, cleaned up all the contacts and put it back but it's just the same. Anyway, I'm pretty sure it's not the cluster, because I checked by swapping th o/s cluster over and that exhibits the same behaviour when on the n/s.
The n/s rear indicator works normally, just the stop/tail that's up the creek