"I think he gave me the wrong plate."
Translation:Jag tror han gav mig fel tallrik.
Note that the adjective "fel" cannot be conjugated.
"The wrong" + singular indefinite noun is just "fel" + singular indefinite noun in Swedish, so it must be "fel tallrik".
the wrong road = fel väg
"The right" however is "rätt" or "den rätta", so there are two possibilities:
the right road = rätt väg
the right road = den rätta vägen