You're probably aware of this but I thought I'd mention it for other readers. That ground wire could be useful to you for the D250SA. If you connect the small black wire (the 'AGM wire') coming out of the D250SA to ground, the D250SA will bulk-charge at 14.7 volts (nominal). If you don't connect that wire to anything, the D250SA will bulk-charge at 14.4 volts nominal. (It will charge at those voltages at the standard 77*F. Actual voltage will vary, as it's temperature-compensated via that temp sensor you tape to the battery)
Also- be careful not to connect the cables backwards. The D250SA isn't reverse-polarity protected (nor is it spark-free).
Also- If/when you charge your truck battery with a shorepower charger, note that the D250SA will sense the charger's voltage and will connect the truck and house batteries together. I used a manual thermal circuit breaker (this one) for the D250SA's positive-cable fuse (at the truck's battery) so I can easily disconnect the D250SA or leave it connected as I desire at the time.
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