I am not a lawyer, so can't comment on whether a green light marked 'power' or similar could constitute an excuse of ignoring ones own due care. However, and I feel I need to be quite clear on this, this crane is on private, domestic property. I only use it myself for my own personal projects. The mechanical safety systems are not warnings, they physically prevent an overload taking place. The only way I could see an overload being possible is by suspending a basket and then filling it past the rated weight limit. Since the mechanical safety systems only prevent pressure entering the cylinder rather than releasing it, if you added weight it would eventually collapse. I don't have a huge amount of paperwork for this crane since its so old but I understand it to be tested to 150% of its maximum capacity. My 'dead reckoning' skills as an engineer mainly engaged in certifying and repairing powered access and site lifting equipment would support this. Of course, if this was something I was doing for my company, I would leave well alone.
Fred - thanks again, I might come back to you on the code!!!