i may be a little late on this response, but to answer your question having a pre 2003 I'm pretty sure your harness is not equipped for heated mirrors. I'm not 100% on this
but on your truck it should be a white cylindrical harness, and on 2003 + it is a dark gray rectangle harness that has everything (signals, markers, mirror motor and heating element supply) all in the one harness, plug and play for any type of mirror and every model F and E series.
This doesn't mean you can't just cut the old harness off your truck and the harness off the new mirror and splice them together along with a 12v supply either switched or on with ignition. Easy enough.
Here is a write up
with some pictures that may help, it's on a 2003 but the only difference is the harness.