The idea is to identify the ground wire FIRST and work from there.
If you are not sure , let somebody who knows do it.
I had success with my 300SE trunk light.
Just an option for your convenience.

(get color codes for your car or use a multi-meter.)

__________________
1979 300D 220 K miles
1995 C280 109 K miles
1992 Cadillac Eldorado Touring Coupe 57K miles SOLD
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1979 240D 140Kmiles (bought for parents) *SOLD.
SAN FRANCISCO/(*San Diego)
1989 300SE 148 K miles *SOLD