My favorite troubleshooting trick. I have done this trick for shorts in control panels at my job many times.

Get your (incandescent) glove box or dome light bulb out of the socket (this works for 124s or older with the bullet fuses, newer cars with the ATC-fuses you have to make a little rig out of a bulb socket and some quick connects)
Put it in place of Fuse #1
Turn on the marker lights
If the bulb is glowing you have a short
When the bulb goes out you have found the short

The bulb gives a safe series impedance to help you find the fault without hurting things.

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The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech