That's the same picture as in reply#22.
The "silver" box (in reply #22.)
The two cables that look like they are plugged into the "silver" box(in reply#22)
(from the right).

IF you are saying that one of them is "86" [gone/unplugged].
That would stop power from being delivered to the interior/dash/console lights.

In your test Today socket #1 is the/leads to Ground ('have to put Positive lead
of DMM on something "HOT"/12volt and the Negative lead into the #1 socket,
with the DMM set to Direct Current)
Socket #2 is the power supply lead to the Window Switch Bulb.If Tomorrow
you find the missing plug/cable(s) and re-insert it(them) into X6/1 [the "silver" box][Barring any other electrical faults]...socket #2 will be "Live"(powered)
and you could use it to test socket#1.
Although by then the lights will hopefully be on.

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'84 300SD sold
124.128