Hi, I have a boiler and tried to get rid of the old thermostat but made the mistake of not writing down where each wire should go. I tested voltage and continuity:

Basement, 4 wires
From Trasnsformer: Yellow and Brown and I tested 26V
From Extra box (not sure what this does) Red and Black wires with Zero Voltage

Main Floor, 4 Wires
Yellow, Blue, Red, Black and there's 26V between the Blue and Yellow wires.

This is the continuity I tested
Yellow basement goes to Yellow on the wall, Red goes to Red, black goes to black. BUT the Brown wire from the transformer has no continuity with the Blue on the wall.

Appreciate any thoughts on how to wire my thermostat

Pictures could be a huge help also any information you can get off that "box".
Gas or oil? How many heating zones? If more than one zone, are there separate circulators for each zone or zone valves? If zone valves, make & model please.

Pictures are best done on a photo hosting site such as photobucket.com or similar & a link to such posted here.