switching from LP/elec H2O heater to just LP

So I had 4 wires feeding my LP/elec water heater, now I have 3 coming off the new LP only unit. There is a wiring diagram with the new unit, but not sure exactly what I have with the old wires. I'm assuming I can just turn on the switch, probe the wires to see which ones have 12v on them and hook them to the new unit's supply wires?

old tank's wiring is:
Gr
Or
Wh
Bl

new tank's wiring is:
Gr
Br
Bl

since im at work now, I don't remember the diagram. It can't be too complicated, right?

UPDATE: just called Atwood, they said the following:

Gr - ground
Or - gas
Wh - elect
Bl - +

so just connect the new like this:

Gr - Gr
Br - Or
Bl - Bl

Sounds simple enough. Also, they said I could flip the switch for LP and I should have 12vdc across the Br to Gr and across the Bl to Gr.

I'll see tonight!