W124 Blade Fuse Box Upgrade Kit Installation Manual

Basic instructions:

  1. Disconnect positive terminal from the battery.
  2. Remove old fuses.
  3. Remove 7 Phillips screws.
  4. Remove the lid.
  5. Take pictures of the existing wiring.
  6. Unscrew all existing leads.
  7. Screw leads into terminals on new board.
  8. Wire up the LED ground wire.
  9. Put back cover back on, re-installing the 7 screws.
  10. Reconnect positive battery terminal.

See @vmrski's installation video on Instagram here: Instagram

Detailed instructions:

  1. Verify all electrics work (or not).
  2. Cover your fender with something so you don't scratch your paint while working.
  3. Disconnect positive terminal from the battery. IMPORTANT!
  4. Remove fuse box cover.
  5. Remove all old fuses.
  6. Unscrew the 7 Philips screws holding the fuse holder.
  7. You will now see the nest of wires in all their glory. If you see any hacky splices, nicked wires, or other things obviously amiss, note them and ensure they get fixed while you're in there.
  8. Start taking gobs of pictures. You cannot take enough pictures. You will most certainly regret not taking more. 
  9. Unscrew the screws holding the wires to the board.
  10. Take more pictures as you progress and more connectors become visible.
  11. Eventually there will be no more wires connected to screw terminals.
  12. Fix any wiring crimes committed by POs (or younger yous) now. Use proper tools and splicing methods. Seriously, don't be that guy anymore.
  13. Connect the wires to the correct screw terminals on the new board
  14. Connect the ground wire for the status LED circuit to a suitable ground point on the chassis. The LEDs will not work (but everything else will) if you skip this step.
  15. Once you are done, double-check your photos. If a little voice voiced uncertainty, listen to it. Go back and check the pictures.
  16. Now test that you did it right.
  17. - Reconnect the positive terminal to the battery.
  18. - Start the car and test that all electrics work.
  19. - Assuming it's all A-OK, button everything back up the reverse of above. 
  20. Celebrate!