Turn signal bulb out but service change the wiring?
Hopefully, that'll fix it for you.
There's a Technical Service Bulletin (TSB) out on the turn signal socket wiring. Many of them have been defective - I had one of mine replaced as well.
Hopefully, that'll fix it for you.
I haven't seen the TSB, but a noneducated guess would be that all W203s and CL203s use the same socket wiring, so all may be vulnerable to this problem. YMMV, though.



