Convolutions with Honeywell

In June I put a programmable Honeywell thermostat RTH2300 in our 1956 home. Sometime in the 90's a heat pump had been installed. The directions for the H'well stated how to wire for heat pumps (p21). The directions also stated it wouldn't work for heat pumps(p.ii). I found the latter true now in December, when I switched to heat, and burned up the transformer but got no heat for the house. So I bought today and installed RTH3100C. The wiring setup from June was long lost. The replacement transformer started getting too hot. I think my meter measured 37 amps on the secondary side. Really irrelevant. What was relevant was some wire to the thermostat was wrong, and was shorting things out. I went to the air handler, and started taking off wire by wire the loads on each color thermostat wire. Each time I did this, I made the secondary (24v) connection to the transformer. Each time there was a hefty spark, indicating I'd yet to pull the offending wire. The B wire was the culprit: I pulled its load off and no spark, and some clicks occurred while the aux heater kicked in. P.12 of the manual clued me in: an optional slot for the B wire is the C terminal. The house is warm now, and the transformer stays cool. Thanks to another post that alerted me to forget about the T wire.