As noted earlier, some styles of fuses are not compatible with the W123 fuse box and should be removed if found in the box during inspection.

These fuses are those made with aluminium, rather than brass. Shown here, you can see that these have a silver color to the metal used.

The aluminium fuse will lead to dissimilar metal corrosion between it and the brass housing, which will lead to a poor connection and a failed circuit.