What’s this part?

[blown motor]

I found this under some stuff on my desk. I think I bought it off a member here. Where does it go?

[Mr Cuda]

Trunk light.
 Part of the wiring has been cut, but popular part

[blown motor]

Where does it mount? I suppose I'll need a switch to make it work.

[Mr Cuda]

There should be pictures of where it goes on the inner trunk lid online.  I have no challengers to reference.
 The light is the switch.  It's one of those banned mercury toggle switches.  All you are missing is the splice connector to plug into the trunk harness.

[Jay Bee]

Proper connectors pictured, and yes, mercury (banned) switch inside housing.
Other info: the feed wire should be about 54 inches long and black for 1970 only, brown for other years. Some non-Ebody cars had a different plug, second picture

[71vert340]

Here's photos showing the trunk light. You can see the bracket mounted in the square hole at top right of photo 1. You can also see the wires exiting trunk lid on bottom left. photo 2 shows light mounted up in trunk lid.
 Terry W.

[70/6chall]

There is a clip that clips the wire going to harness to the trunk hinge.

[blown motor]

Thanks for all the information guys.    Now I have one more thing to tinker with this winter.

Can someone explain how that mercury switch works?

[MoparLeo]

Orientation/gravity.
 Mercury is a conductive metal that is liguid at normal temperatures and very poisonous.
Imagine having a bottle with a bare wire at each end inside.
With the bottle oriented with the wires at the 12 & 6 o'clock positions.
Now fill the bottle 1/2 way with a liquid (in this case it is Mercury).
Tilt the bottle to one side until the liquid now covers the bare wires on each end.
 This would cause a physical connection between the wires.
https://www.elprocus.com/mercury-switch/

[blown motor]

Orientation/gravity.
 Mercury is a conductive metal that is liguid at normal temperatures and very poisonous.
Imagine having a bottle with a bare wire at each end inside.
With the bottle oriented with the wires at the 12 & 6 o'clock positions.
Now fill the bottle 1/2 way with a liquid (in this case it is Mercury).
Tilt the bottle to one side until the liquid now covers the bare wires on each end.
 This would cause a physical connection between the wires.
https://www.elprocus.com/mercury-switch/

Interesting. So I should be able to test this switch by putting 12V too it and grounding the bracket and tilting it in different directions?

[MoparLeo]

Yes.

[Jay Bee]

So I should be able to test this switch by putting 12V to it and grounding the bracket and tilting it in different directions?

As said, yes. Just ensure that you orientate the tilting similar to that of it screwed to the trunk lid.

[Jay Bee]

Picture of it plugged into the car's rear harness & something I drew up (measurements are from an OEM I sold)