Hi Laurence
Your problem is a built in safety device. The system is :FAILING TO SAFE; The reason for this is varid, but to start with it is most probable one of the comutating devices, which consist of the following, DIODES, THYRISTORS,CAPACITOR BANK. OR MOTOR GROUND FAULT. As you are in the biz these can be checked with a multimeter. Be aware though that as the SCR's thyristors are high on the list a small battery and bulb will clear them to clear working order, when gated. Not sure if I still have drawings as I am half packed to move house in a few weeks. If you are still stuck let me know and you can contact me and I will talk you through. Also make sure you isolate the pigtails. Another problem could be the overcurrent relay located under the right hand floor plate, and if the battery is low as you say the volt drops on lifting this could also be a factor. This hytronic system relies on pull-in and drop-out voltage of the operating contactors, so any volt drop will affect it. There are a few more obscure faults that will cause this fault but these are the most common. Good luck