I have a question regarding a Honeywell Thermostat installation.

The model is a Honeywell RLV430 and is connected to a forced air heater system with two heater units.

I installed the previous model (about 1-yr ago) after I had removed the contractor's Cadet dial thermostat and wired it the same as they had. This morning I woke up to the heat blasting, the smell of smoked wiring, and a blank, unresponsive thermostat. I secured the breaker and removed the thermostat to find the wiring on the thermostat side burned back, the solderless connector melted, and the thermostat possibly DOA. I purchased another of the same model (there aren't many forced-air stats out there to choose from).

Now my question.

The wiring inside is copper with black sleeving. Three wires - ALL BLACK! The socket has two pass throughs with one wire coming from the right and two from the left. The old stat was hooked up like this: 2 left coppers + 1 stat wire and 1 right copper + 1 stat wire.

The installation instructions cover a 2-wire and 4-wire installation and this appears to be neither and both at the same time. The rest of the house's stat boxes are standard 2 wire. This one has me confused and leery considering my recent smoke-out!

Please help me wire this!

Here's a picture of the wiring box. The two left wires both come from the left tube seen in the upper left corner and the other black wire (going to the right) comes from the right tube seen in the upper right corner of the box. The white wires are a mixture of both and there is a bare (ground?) wire in the back and bottom of the box. The tip of the middle wire is snipped from my removal of the burnt wiring.

I tried to hook up the connections as follows with these results:

Far left black wire with the right black wire + stat and the middle + stat = working stat and heaters but the stat in the adjoining bathroom did not work. Also, the room stat seemed to feel warmer than normal but that could be my blooming paranoia. I also thought I smelled something but it could've been a new circuit board in the stat or remnants of the old smell.

Original (1 far left black + stat and 1 right black (the left one in the picture) + left black + stat = working stat and heaters and the bath stat worked as well.

This has me thinking that the original stat just went bad and that the wiring was all right but I would like some (semi) professional assistance on this one.