When I wasn't getting anything but the fan to run as I ran up the line voltage, I ended up replacing the lamp socket assembly, since I had managed to crack the ceramic housing of the original lamp holder. That hasn't changed anything...I've either killed the Triac, or....it being connected as my diagram shows (that being the original wiring for the other Triac), it isn't correct for this Teccor Q4010L part. Take a look at the notes on pages E2-5 & E2-6 of the Teccor data sheet as reference, where MT1 is shown as GND, the Gate pulse is of the same polarity as that of MT2. Do I indeed have this wired wrong (though was correct for the other part)? It's always the 'simple' stuff I can't figure out!