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. Check below for specific instructions for your fuse box.
  7. Move wires from the old box to the new box.
  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. Look at the specific instructions below, some cars require slight installation differences.
  8. 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.
  9. Start taking gobs of pictures. You cannot take enough pictures. You will most certainly regret not taking more. 
  10. Unscrew the screws holding the wires to the board.
  11. Take more pictures as you progress and more connectors become visible.
  12. Eventually there will be no more wires connected to screw terminals.
  13. Fix any wiring crimes committed by POs (or younger yous) now. Use proper tools and splicing methods. Seriously, don't be that guy anymore.
  14. Connect the wires to the correct screw terminals on the new board
  15. 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.
  16. Once you are done, double-check your photos. If a little voice voiced uncertainty, listen to it. Go back and check the pictures.
  17. Now test that you did it right.
  18. - Reconnect the positive terminal to the battery.
  19. - Start the car and test that all electrics work.
  20. - Assuming it's all A-OK, button everything back up the reverse of above. 
  21. Celebrate!

 

IMPORTANT SPECIFIC INSTRUCTIONS

Look at the back of the stock fuse box for the part number on the main box (below B/C), it will be one of

  1. 124 540 01 50
  2. 124 540 12 50
  3. 124 540 20 50

 

Then, remove the side section for EFGH by carefully poking at the clips with a screwdriver. On the left side there may be a connection between F and G.

Some connected units will have a strip running down the whole length similar to the first photo. The connected unit pictured above is from a -01 50 box.

Instructions:

If there is a connection between F and G on the side section, install the included red cable between the two screw terminals for EF and GH on the back of the new fuse box.

If you have main box # - 20 50, continue installing.

If you have main box # - 12 50, install the small green 30A fuse in the A1 jumper on the back.

If you have main box # - 01 50, first install the A1 jumper similar to -12 50. Also, the -01 50 units are built differently than later models, both visually and electrically. It has the curved spring sections on the bottom instead of the top, and the fuses sit horizontally instead of vertically (see pictures above). Electrically the input and output of each fuse is swapped, so you need to swap the pairs of wires for each fuse when installing the new board. Only swap wires for fuses that have two screw terminals (skip DEFGH, they're always wired the same).