good luck man! I have been attempting to answer this same question for weeks. Mine needed replacement and I could not read the size. Replaced the one on the left(when under trailer looking forward) with a 40, Replaced other with a 20 but I believe is too small. It operates the slide out and kicks off. My trailer is stored 250 miles away so I have to wait to change again. A friend who is a home electrician told me if I can't find the answer, to move up to the next size to see when it stops tripping. Best advice I got so far.