I have an old house and hooking up dryer wire in new box. I have a black wire and 2 white wires - how do I choose the red for the correct terminal of the new receptacle. I cannot run a new wire at this time. Oh, there is no ground wire.
Thanks

Are these wires in conduit, cable, what?

What size wires are they?

They are in steel armor sheathing. They are 8 of 10 gauge stranded wire.

So you have BX or MC with one black and two whites?

The metal sheathing may be the equipment ground, if that cable is listed as such.

Perhaps if you look close, or strip more sheathing, you may find that one of the whites is actually a red, that has faded to white, I have seen that happen often.

Otherwise, you will need to ring out one of the whites, and relabel it red, and you will be all set.