You'll have to run wires from the a/s shifter to a plug underneath the dash.
The C106 connector to be exact - see FSM schematics, connector location diagrams, and connector pinouts for details. That connects the shifter upshift (light green/red) and downshift (yellow/light blue) wires to the PCM (TCM in earlier years). I think the wires are already run from that connector to the PCM - some earlier years they are not - but if they are not, you'll have to make that run too (could make one long run from the shifter switches directly to the PCM, i.e., bypassing the C106 connector) if that's the case. But I think for '02, the C106-to-PCM connection is already made.
There are no connections between the shifter switches and the cluster.
The other two connections you will need to make are the power and ground for the shifter switches. Some people tap into those at connector terminals at the BCM, but my preferred way are to grab power by tapping the red/white wire (+12V power) at the DLC connector and, for ground, put a ring terminal on one of the two ground studs on the gas pedal side of the floor/console hump (you can see it by peeking behind the bottom of the console plastic next to where your gas pedal foot ankle would be).
That's 4 wire connections (two shift wires, power, ground) total to be made. You'll be fine as long as you get the shifter switch connector with a few inches of its 4 wires attached to splice to.
Except for the ring terminal ground connection, you can T-tap to the existing wires - USE RED T-TAPS ONLY
. They are the correct ones for all of those wires. Blue T-taps are for larger wires and the connections would be very unreliable. If done correctly, the red T-taps would make a reliable connection. You have to make good crimp connections. The other option (if you lack confidence on the crimp connetions) would be soldered splices.