The clock does get 12V, however I do not think it comes from the amp gauge. I looked at 2 different wiring diagrams; one for a 73 Cuda and 1 for a 70 challenger. In the 73, it only a clock on the rallye cluster which shows a "battery feed" which is a independent feed line in the harness. On the challenger it connects into 12V cluster that feeds a number of things. All that said, I suspect any 12V source will work, however given the issues that could occur with the amp gauge I would select some other source of constant 12V.