I had a weird problem today, went to start my car and all the gauges pegged out and it fired up and ran way rich. I found that the fuse for the gauges was blown, so I replaced it and it ran fine, my question is what is also running on the gauge fuse circuit that controls the mixture?

 

There are several minor circuits running off the gauges fuse. Your rich experience probably was an indirect result rather than a direct result of that. Off the top of my head the TCC lockup, neutral safety switch, but there's a couple others, too I believe.