How does Ernie Isley get the sustain sound on Lead guitar Who that Lady and Summer breeze?

Ernie Isley doesn't play lead guitar on either song. His younger brother, Randy Isley, played the lead guitar part on both songs. They were recorded at the tail end of an era when guitar sustain pedals were uncommon. What Randy Isley did was fingerpick the notes on his Gibson ES-335 guitar and gently rolled the volume knob up and down to achieve that lush, vocal-like sustain.