the problem may be simpler.
The wire runs around the hinge of the trunk.
Often the wires get weak and break due to the
constant bending.
Try grounding the circuit on a body part and see if the light works.
If it does, then splice a new ground wire before the
harness bend at the trunk (boot) lid hinge

Good Luck.

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