Re: grounding addition amplifier......With second battery.
Some ground to battery with high power or competition setups but others say it makes so little difference when metered it's not worth the added expense. If your second battery is close to the amp you could wire it either way with same results.
'05 F250 King Ranch Crew Cab 4X4 Off Road Modded Powerstroke
Rebuild in process
Pioneer DEH 80PRS
Modded Linear Power LP4753IQ
Front Woofer: Infinity Kappa Perfect 6.5"
Front Tweeter: SEAS Neos in pods
Back: Pioneer TS-D6802R
Knukonceptz Karma 12ga
Stinger HPM3 RCA's
Big 8: PhoenixGold Oga