Not just hyd pressure, Air and the various Gasses used everyday are as dangerous it only takes 4psi to pass through skin. If I remember correctly. Its a minefield out there.
Give it time and all of a sudden you will just click with the gearbox and you will wonder what all the fuss was about. Its a slow truck and empty so it does not roll well just keep the revs down because the old AEC pulls for fun. Revs to road speed you cannot get your technique right untill you get some time behind the wheel.
With the black probe pushed between the points it is closing the circuit and will be giving you false information. Is there any power at the leads you have taken off the dynamo. Do you still have the power drain without the dynamo?
Welcome in. A QL. not for the faint hearted. Many QL owners on here. I did hear of a QL tanker in a field in Staffordshire, but I do not know precise location.
Are the points closed on the relay. Take the power lead off the dynamo put a meter between the wire and the terminal on the dynamo to check there is no current flow with the engine off. Also do the same with the power input on the ignition coil to make sure there is not a small leak from the ignition switch.