Water heater swap out, newer for older

[Curtis Kotter]

Maybe someone can help me with wiring a replacement water heater in a Springdale. I removed a Dometic GCH6A gas/electric combo, due to a crack, and am putting in a used Dometic G6A gas only. Replacement unit purposely doesn't have an orange or yellow wire for the electric switch relay, but it does have 3 wires: Grey, Green, and Blue. I'm confused because the 12v side of the trailer wiring has Brown, Grey, White and Blue. I have one too many wires (as expected with omitting 110v) but I don't know how to tie up the 3 wires on the heater and which of my trailer wires to omit/cap. I got a wiring sheet from Keystone and got even more confused because their color scheme for water heater is White, Brown, Orange, and Pink. The diagram sticker on the replacement heater is worn so I can't really tell how they designate the colors. Can anyone shed light before I blow myself up or ruin another heater?