Hi!
My English is still quite bad, so I use g-translator, so I apologize if what I wrote is grammatically incorrect!
First of all, I would check the body points of the lamps (there must be a black box or screw on the extension directly behind the lamp, to which other black wires go). If the grounds are good, I would look at the lamp sockets next. If they are also perfect, then I would look at the relays next. If there are no problems with these, then the steering wheel switch remains, but it is tricky, since the base of the steering wheel switch is one with the airbag transfer belt (unfortunately, the two are not available as separate parts, so even when disassembled, there will not be a functioning airbag belt).