away from the header thus urging the hook 157 of the latch finger 156 from connection with the lock recess 150 in the wall element 114 further force causes the cover plate 106 to pop out from the channel 122 and be removed from connection to the header the hooks 155 and 157 and lock recesses 150 could be reversed wherein the hooks are on the wall elements 110 and 114 and the lock recesses are in the latch fingers 154 and 156 similarly the ribs and grooves could be reversed wherein the ribs 148 extend outwardly from the wall elements 130 and 132 of the post beam 136 and the grooves 146 are in the wall elements 118 and 112 of the header beam further an appropriate opening or cutout 160 is provided through the wall element 114 of the header beam 138 b the cutout being proximate to the inlet into the channel 122 and in that portion of the wall element 114 that is defined between the wall elements 118 and 116 the cutout 160 allows one or more wires w of a wiring bundle to be turned 90 u00b0 relative to the passageway 128 and directed vertically downwardly and into and through the box chamber 140 of a post beam 136 as shown in fig2 two laterally spaced post beams shown in dashed lines are connected to the header beam and the wall element 114 of the header is provided with two laterally spaced cutouts 160 a and 160 b each cutout 160 a and 160 b is positioned for directing one or more wires into the box chamber 140 of a respective of the laterally spaced first and second post beams as shown.