Fuse A 16 Amp
Fuse C 8 Amp

There is a connector, X86 from which the Trunk MS gets Positive (12 Volt D.C.)
power.The wire is Red with a White stripe and is .5 mm in diameter.
(Terminal 2 on the Trunk MS)

There is also a Brown (Ground) wire that connects to ground at W12.

There is also a Yellow .5 mm wire that connects positive to the Vacuum Pump
to Unlock the Actuators at each location.

Turning the key to UNLOCK routes positive power from the Red/white wire to
the Yellow wire.
Turning the key to LOCK routes power from the Red/white wire to Ground @ W12


X 86 is described as "connector,central locking system 3 pin"

I'd start by checking X 86 for: Power, Continuity to Ground on the applicable
cables.
Then check the Electrical connectivity/continuity of the Trunk Micro-Switch.

Out on a Limb ,Here...
I suspect the "Hack" installation allowed the Rogue Electrons to FRY the MS
or disable one of the Wires.

Hey, This may be your lucky week and you'll find the Electrical Clownistas have only disconnected X 86 !

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'84 300SD sold
124.128