2002 buick rendezvous both electric seats quit working fuses OK switches work and lights come on. I am mechanical but if anyone has had the same issues I may save a bunch of time looking.

This seems to to be an issue with some Buicks. I don't think Buick have a specific fuse for the back up lights and the 2005 to 2007 Rendezvous models had a relay for those lights.
OK. Start with the simple and silly stuff first. Check the bulbs and the sockets they fit into. It could be a blown bulb or there is dirt and corrosion on the contacts blocking the electrical current to the bulb. Using a multimeter set to DC volts test the bulb socket for power to the bulb. With the Park brake ON, the Ignition ON and the Engine OFF selecting reverse should turn the back up lights on to test for power.
If no power to the light fitting next move to the switch on the Transmission the shifter operates when you select reverse. I'm not sure where it is on the Rendezvous Transmission, You might get lucky and it'll be screwed into the housing next to the actual shifter.

Looks like fuses 30 and 41

View more images Web results

Buick Rendezvous (2002-2007) fuses and relays

https://fuse-box.info > buick > buick-rendezvous-2002-...
Fuse box diagram - Fuse Box Location. It is located in the passenger's side of the center console near the floor, behind the cover.

.

Could be the rocker switch panel or the electric motor inside the door ,check for power with a test light.

The ABS dashlight is to inform you that your automatic breaking systems need maintenance. Because this is your breaking system you don't want to wait, take it to the mechanic and have it checked. or you can get a code reader to clear the fault codes.

check electrical connections between battery and fuses in engine compartment, check connection at starter

There is not a fuse listed for heated seats but fuse 16 is for heated mirrors and fuse 11 is power seats. i'm guessing one of those should also control the heated seats.

look for rear wiper fuse and relay.because both circuits is tie together . look in glove compartment for the manual .it will show where all fuses and relays located.

ASE mechanic:
blower motor regulators go bad because of the switching between low and high speeds. some times these are under the dash and require tiny hands and lots of patience.