The higher wattage will eventually damage the wiring, the lamp socket and may melt the plastic nearby. For some improvement in your lights, you can use the Sylvania Silverstars. They are not too expensive and you can often get them on sale with a rebate. I have them in my 300E and my Volvo 940. They are not as good as the Euro standard lights but much cheaper.

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1986 300E
1993 Volvo 940 Wagon
1984 Volvo 240 (daughter's)
1976 Dodge 1/2T pickup, gas hog