As far as turn signals you may want to check the 4 way hazard switch. If this switch is bad the turn signals will not work. As far as the other dash lights I would suspect a bad ground for the instrument cluster (a common problem for W123 cars). Remove the instrument cluster and attach a new ground wire from the back of the cluster to the ground point on the steering column support. Mercedes uses brown colored wires for ground. Make the wire long enough to ease future removal on the instrument cluster.