I recommend you research posts Guyfang posted. He posted everything you need. Step 1; What type do you have, TRC or Libby. (TRC black or green Libby regulator). only replace with same type. Step 2: PN: 19870 is TRC, and PN: 122-3054 is Libby. This is just the regulator. DLA Avaition put together kits after countless requests from LARs that contain everything you need to change from one to the other, but no Part Number you can actually get outside the Military system. The following are different between the two: Regulator, Voltage adjust rheostat, R-16 located behind the green CKTBKR panel, and the power sensing transformer. Libby trans have black terminal boards and TRC has just connecting loop terminals. Mixed up and you will have EXPENSIVE issues.