In Mercedes The Brown lead is ground. Brown standing for Negative Earth.

I did say you can ground it by attaching the ground to some metal. which is the easiest way to do it.

It is always a good idea to test with ignition on and off, some things will change polarity like you said when key is on or off.

I myself use a multimeter and test for voltage, test lights are simple and cheap and work similar.

I myself have never blown a fuse installing a radio, though I did once hook up the ground to the illumination wire and fired a radio. This was of course the first and only time it happened.

Alon

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'92 300CE
Metallic Black (Blue Flaked) on Parchment
Clear Corners
94-95 Tail-Lights
Debadged
Black Grille Insert
78.5k Miles

Future Upgrades:
Sportline Suspension
17" AMG Monoblocks or EVO II's
Euro Headlights
Performance Chip
AMG Exhaust

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