Terminal mechanic reported while working alone troubleshooting a flight control hydraulic leak; was told to find leak with hydraulics pressurized without flight control locks. Mechanic decided to write up an item as an educated guess because they did not feel safe working alone and in a dangerous situation.

Narrative

Mechanic with approximately one year was working the terminal and had an extra plane dropped in around XA:15. There were not enough people here to work in pairs. There was a hydraulic leak coming from the RH wing outboard and middle canoes. Mechanic was put on the plane to find the cause of the leak. To find the leak they needed to run hydraulics and lower slats and flaps. They were alone 90% of the task and were told to find the cause of the leak before the plane could be sent to the hangar. They spoke to the leads and were told that they could not send the plane there without finding the leak; The mechanic ended up having to stick their head in the lowered slats with hydraulics running and no second person watching the control in the flight deck. At one point Mechanic had a box guy out there to run spoilers so we could check for active leaks there. He was only able to stay for about 20 minutes.After feeling very uneasy and unsafe Mechanic decided it was best for them to make an educated guess about where the leak was coming from; so they did not have to put their head in flight controls with hydraulics running. The supervisor then asked them to go back out there and get better pictures of the leaking component and make sure everything would be clean for the hangar. Mechanic told him I was not going to put my head back up there and that he needs to send the plane down to the hangar.Mechanic wrote the item up as an educated guess because they did not feel safe working alone and putting their self in a dangerous situation.Mechanics are often pressured to do things at the gates; which can result in injury. Leads lets the supervisors dictate maintenance and will not stand up for us or our safety.Supervisors need to use proper channels of communication. If there are not enough people to work a job for safety reasons. The job can wait. AND never should any Mechanic be sticking any body parts in flight controls with hydraulics running. LOCK OUT TAG OUT!