Wessels, 24, was found guilty by a URC disciplinary panel of "grabbing, twisting or squeezing the genitals" of Connacht flanker Josh Murphy when the Bulls edged a narrow win in Galway on October 17.
He denied the action, which was not spotted by the match officials and for which there was no video evidence. The complaint came via the citing commissioner.
The disciplinary panel sided with Murphy, who had received a red card for striking Wessels at the ruck, which was expunged following Wessels' guilty verdict.
The 24-year-old Springbok appealed the decision and while this was dismissed, an independent appeal committee found the original panel had erred in their nine-week suspension and did not take into account Wessels' conduct, reducing it to eight.
It means he will miss the Springboks' five matches in the Autumn International series, starting on Saturday against Japan.
"After reviewing the grounds of appeal and hearing from the Player and his Club the appeal committee dismissed the substantive grounds of appeal, but reduced the ban by one week," a statement from the URC said.
"The panel did so on the basis that the initial reduction from the low-end entry point (of 12 weeks) did not take into account an aspect of the Player's conduct in the context of the case.
"The Player will now miss eight games and will be free to play from December 20."