Greetings,

I purchased a factory fog light kit for my '04 Silverado from a vendor on
eBay and installed them myself.  It came with the lights, harness and new
dash switch.

Now making the presumption that the Trailblazer is built on the same type of
architecture as the Silverado (namely, Plug-and-Play) then once you get the
kit in hand simply install the lights as instructed (you may have to cut out
the holes for the lights in the air dam like I had to or you can purchase a
new air dam with the holes and spend more money) and run the wiring harness
to the underhood electrical center.  Typically, you will have to raise or
rotate up the circuit block to access the underside where you plug in the
ends to the harness.  Reinstall the block and plug the relay into the proper
slot.  Be very sure where you are installing the harness ends under the
block as the directions were a little confusing and the diagram wasn't at
all clear until I realized that it was showing the other side of the block
and not the side I was working on.

A new switch for your dash may also be included, which will require you to
remove the dash bezel and install the new switch (also PnP).  The switch may
be a seperate new unit or a replacement for one you already have that adds
an additional switch for the fog lights, as was mine.

Now comes the tricky part.  The Body Control Module (BCM) may or may not
already be programmed to accept fog lights.  If your new lights work then no
problem, but if not then you need to check all connections and proper
placement of the harness ends in the circuit block and if all that looks
good then go to somewhere that has the proper computer that can set the BCM
to recognize the fog lights (usually the dealer, for a small fee of course).

The complete install on my Silverado took about 90 minutes, with the hardest
part being removing, cutting cleanly into and then replacing the air dam.

Cheers - Jonathan