[cclark26]

I was changing out doorbell. I marked the front, rear, trans wires but when I pulled the wires through the hole my markers came off and now I can't tell which wire goes where.

[Stratmando]

Look for voltage on a pair, that is transformer, connect 1 pair as front door and remaining pair as back door, If You want to swap chime sounds for front and back door, swap front and rear wires on chime terminals.

[hkstroud]

Connect transformer wire to transformer if not already connected.
Remove front door button and connect wires together.
With meter check for voltage between wires.
Label the two wire which show voltage A and B.
Label third wire C (C will be rear door).

Disconnect wires at front door.
Connect wire at rear door.

Check for voltage between A and C and between B and C.
The wire that shows voltage will be transformer, the other will be the front door.

[KISS]

Connect any two wires to front and C terminals.

If nothing happens when you push the front and rear buttons, then the other wire is common.

Then start identifying the door.