@alanmcm
Like has been mentioned, you are undertaking work that you are not competent to do, your willingness to learn commendable but this area of the industry is heavily regulated, a simple act of added to or changing the function of a machine/control requires a full risk assessment, what may seem trivial in alterations can have requirements that require new safety measures and systems to be put in place.
Even the simple addition of extra actuators like a few E-Stops to a simple DOL starter for a motor can require the whole control system to be redesigned so as to comply with the relevant standards.
The minute you enter a control board and make alterations and/or additions you take on board the responsibilities that said machine is safe to use, meets current regulations and has all the documentation and risk assessment that comes with the work you did, if you work for a company and you are been asked to do this then you must make it clear to them that you are not competent in this field and you have no qualifications to show you have had the training.
If you are ever in the unfortunate position to be pulled into interview due to an accident on a machine you worked on, you will be required to show your competence, show how the machine operates and how the safety features of the machine work in conjunction with the operator, if it is found the risk assessment falls short, the machine has been illegally upgraded or repaired then you will not have a leg to stand on legal action may be taken directly on yourself and/or the company you work for.
In the past the company I use to work for was caught up in such a scenario, we had to show how the safety system worked, what safety level it had been placed under and we also had to show them how why we thought the operator get injured also why and how the safety systems failed to prevent this... lucky for us we had complied and assessed the system correctly and we showed the operator had used ladders to climb over active safety barriers, opened a ducting panel using a tool and tried to unblock ducting while the machine was running, he failed to realise the fan blades spinning at 1500rpm may come in automatically! The said company was given a very large fine for not training it's operators properly and allowing routine breaches of safety, the point I am making here is you need to know your stuff from the the associated regulations, how to risk assess a machine and know what level of safety it will fall under before you even consider trying to work on it, the closest you may be able to go is to replace a like for like part due to failure where you have made absolutely no changes or additions and again if the machine is unsafe even ignorance can come back at you if anything were to occur.