The car is my '94 E320 wagon and when I lift the back hatch all the way the cabin light in the rear part goes out and the dash lights that control the seat heaters, snow tire chain light and rear window wipers become lit.
If I don't lift it all the way everything is normal. Where is the contact or electrical parts the control the light switch?

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dtf
1994 E320 Wagon (Died @ 308,669 miles)
1995 E300 Diesel (228,000)
1999 E300 Turbodiesel ( died @ 255,000)
2006 Toyota Tundra SR5 AC 4X4 (115,000 miles) rusted frame - sold to chop shop
2011 Audi A4 Avant (165,000 miles) Seized engine - donated to Salvation Army
BMW 330 xi 6 speed manual (175,034 miles)
2014 E350 4Matic Wagon 128,000 miles
2018 Dodge Ram 21,000 miles

I'd bet you have broken wires between the body and the tailgate.

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1989 300 SEL that mostly works, but needs TLC

Trunk wiring problem

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95 E320 Cabriolet, 159K

Excellent! Thanks Kestas. I guess I'll have to peel back the rubber boots at the top of the hinges and inspect the wires on both sides. With the switch off there is no problem by the way. The lights stay off.

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dtf
1994 E320 Wagon (Died @ 308,669 miles)
1995 E300 Diesel (228,000)
1999 E300 Turbodiesel ( died @ 255,000)
2006 Toyota Tundra SR5 AC 4X4 (115,000 miles) rusted frame - sold to chop shop
2011 Audi A4 Avant (165,000 miles) Seized engine - donated to Salvation Army
BMW 330 xi 6 speed manual (175,034 miles)
2014 E350 4Matic Wagon 128,000 miles
2018 Dodge Ram 21,000 miles