Mike,
If you have the Single BCC like mine, one relay works from a momentary switch. This means it only needs voltage applied when you want to either connect or disconnect. This is obviously for the battery disconnect. There is another relay called an isolator relay. This is continuous duty. This means there is constant voltage to it when latched (Batts are connected to each other) for the purpose of charging. On some systems there my also be a momentary switch for aux starting when the chassis batt is low or dead. This relay will he warm or even hot to the touch when working properly. The third relay is called the BIRD (Bidirectional Isolator Relay Delay). This is part of the circuit board with the fuses. The senses the voltages of the converter and both battery sets and will energize the isolator relay based on voltage.
As far as your power cord sparking, sounds like you may have additional problems to isolate before you look at your BCC. More info would be helpful.
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2020 Grand Design Reflection 315RLTS
2019 GMC Sierra Denali Duramax
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