In late 1978, partly due to being introduced by the Studio 54 sound system, Hartman reached No. 1 on the Dance Charts with the disco single "Instant Replay" (the title track of his third full-length album "Instant Replay") which crossed over to No. 29 on the "Billboard" Hot 100 in 1979 and also reached the Top 10 on the UK charts. Musicians Hartman worked with on the associated album included Vinnie Vincent and G. E. Smith. This was followed by his second chart topper, 1979's "Relight My Fire" (the title track of his fourth full-length album "Relight My Fire"), which featured friend Loleatta Holloway on vocals. An instrumental version of the song later became the theme for the NBC talk show "Tomorrow." He wrote and produced the 1980 Disco hit "Love Sensation" performed by American R&B singer Loleatta Holloway. The same year and in 1981, Hartman was among the lineup for Hilly Michaels' albums "Calling All Girls" and "Lumia" respectively.