I'm having a similar issue that I'm not seeing stated exactly here. I have 4 connected strings of 50 LED lights that have worked for the last 2 years. After pre-testing and hanging all 4 strings initially worked. However, after an ice storm I noticed that the 2 last strings were out. When looking more closely, the bulbs were actually on but extremely dim. I replaced the fuses on string 3 (the first string with dim lights) and this did not solve the problem. I then ran an extension cord, disconnected string 3 from string 2, and plugged string 3 into the extension cord. Upon doing this, string 1 & 2 remained lit while now string 3 & 4 also lit fully. When looking at the female end of string 2 (where string 3 plugs in) there are no fuses like on the male end. In fact, the end seems completely incased. Also, these 2 connecters were covered together with electrical tape which should have been a water tight seal.
Any idea what my issue is?