Four coach batteries, terminals have 2 cables attached linking the batteries. One battery terminal has a third "extra" cable (much thinner) on the negative post...circled in photo.
What's this "3d extra" cable for?
__________________
DC & Mac
2019 Vista LX 35F (Cayenne)
"The Okiebago"
That looks like a temperature sensor. I assume you have an inverter and this is connected via that data cable to your inverter. The plastic thing is the temp sensor.
__________________
2017 Winnebago Adventurer 37F
2024 Lincoln Nautilus Hybrid Toad
Battery Cable Question
Linear Mode
