Although I agree with the advice to seek out someone locally who can answer questions, if you need printed material, you might consider text books aimed at industrial electricians.
I suspect that the diagrams you are confronted with are more electrical than electronic in nature.
If that's true, then information written for electricians might help you more than that designed for engineers who engineer a system.
A used, 1st, 2nd or 3rd (1993) edition (now out-of-date) of "Industrial Motor Control" by Hermann & Alerich has a lot of information on motors and the control circuits for them, written to be understood by electricians.
There is a whole series of texts on specific electrical subjects published by Delmar, the Electrician's Technical Reference series. I have "Industrial Electronics" by Stephen Herman on my desk at the moment.
Delmar is at
I tend to look for used copies on half.com, ebay or abebooks.com, but you can decide how you want to acquire books.
If what you are looking at is Programmable Logic Control (PLC) circuitry, known as 'ladder logic', then the first couple chapters in a PLC text book would help. Frank D. Petruzella or John W. Webb are two PLC text authors (titles will include 'Programmable Logic Controller'). Someone's borrowed my copies so I can't quote a title for you.
Dan