The rebuilding of dual cab Class 6E1, Series 2 to Series 8 locomotives to single cab Class 18E, Series 2 locomotives commenced in 2009, with their running numbers beginning at 18-600. The rebuilding included the installation of Alsthom micro-processor control technology and was done by Transnet Rail Engineering (previously Transwerk and later Transnet Engineering) at its Koedoespoort shops in Pretoria, Gauteng. In the process their number 1 end cabs were stripped of all controls in order to have a toilet installed.
18-683 was rebuilt from Class 6E1, Series 3 E1375 and commissioned in 2012.
See also the Wikipedia article on the South African Class 18E, Series 2.