My Trane Condenser unit has 3 capacitors - a Start cap each for the condenser and the fan and a shared run capacitor. The system stopped working and I obtained new equivalent Dayton caps to replace the GE ones that were on the unit. The problem is my new Dayton capacitors don't have the terminals marked. How do I identify them to make sure I don't wire it to run backwards?

Sounds like you have two single caps and a hard start kit. On the single caps doesn't matter which connection you use. Dual caps will have C, Herm and Fan.