Date registered: Oct 2013
Vehicle: A200 Sports Coupé C169 2006
Location: Bozeat, UK
Mentioned: 2 Post(s)
Quoted: 207 Post(s)
OK, if the fuse is fine, and the W37 is not corroded, then most likely the blue/grey middle wire is shorted.
Ring the brown wire to ground point
Ring the green/black wire to fuse 37
Check the voltage on the power socket (cigar lighter)
If it shows correct values (about 14.3V when ignition is on, and about 12.6V, when off), then at least you know your power socket is okay.
Check the impedance between the blue/grey middle wire and the brown wire.
I suspect it might be negligible ...
If that's the case, it is shorted somewhere. If no other 58d consumers are affected, i.e. all instrument lights and ambient lights function correctly, then I would suggest cutting it off of the middle pin, isolating it properly and linking the green/black pin with the blue/grey pin. You light will be on permanently (so again, get an LED bulb), but it will do the job.