That's what we figured... (we being another hgv licenced driver who initially raised the defect about a month ago and myself.) Yellow faults can generally wait until the end of day (lighting failures aside), and red faults should be at the very least checked out prior to using it.
Our vehicles all used to be regularly and reliably maintained by the site MT department. But to save costs, the company employed a car mechanic to look after the fleet with a van and no workshop. With this in mind, the only maintenance that is permitted on site are emergency work, ie to get the thing moved out of the way and minor running repairs... tyres/bulbs and the like.
Since this happened, the whole fleet has gone to shit as he can barely keep up with the minor items... the bigger jobs simply get ignored until something breaks or you threaten to report it to Site Ops... then it goes into MT
Refusing to drive vehicles doesn't work, as there's always some dickhead who will take anything out even if nothing works and the wheels are missing