My 2004 buick rendezvous dash lights only half work and all of my air control lights are not working and my rear hatch will only open with the fob. My gas gage also done work right one minute it full the next min it's empty!

Well the dash lights are bulbs that need replaced and with air control bulbs are out also. the fuel gauge is one of two thinks..first is level sensor in the tank should be replaced first also the cluster has stepper motors that control all the gauges $75 to $100 dollars and the cluster assembly can be sent out and repaired to correct those issues.the tail gate touch pad is in need of replacement also hope this helps

It's most likely the wiring harness that runs under the body and up through the floor, located under the driver seat. Search online and you will find discussion and repair videos to help you with your issue.

1) Rear hatch problem: Try unlocking the doors with the switch on the passenger door, if it doesn't unlock the rear hatch then you have some kind of ground or fuse problem with the door unlock switches. Do the lock switches on both the driver and passenger door unlock all of the doors, but not the rear hatch? If so, there's a problem with either one, or both, of the door unlock switches. If you want to check your fuses, use a multimeter to check for continuity on your fuses if you remove them one at a time. Remove each fuse, check to see if your multimeter beeps, when set on OHMS, for each fuse. If it beeps, this means the fuse is good. I agree with checking the internet and use some keywords to describe your problem. I diagnose problems with my Rendezvous using this method. You'll be amazed how many people go into a a lot of detail describing how to diagnose and fix electrical issues.
2) Dash lights / Fuel Gauge problem: If the lights go on and off intermittently, and the fuel gauge doesn't read properly, you could have a ground problem in a wiring harness. If you fix some issues, but the fuel readings go from full to empty, and you know you're gas tank is full, you likely have a problem with the fuel pump assembly in the tank. There's a float mechanism attached to the fuel pump and it sends an electrical signal to the dashboard which displays the fuel level. Either this float can be sticking, due to contaminated fuel, rust, debris, etc. or the wiring harness coming from the tank has a short and is causing the erratic fuel readings. It's a pain to replace the fuel pump because you'll have to remove the fuel tank and access the pump from the top of the tank, but it's easy to remove and replace the pump itself. A new pump will cost about $200.

Have you checked your fuses? Sometimes if a fuse goes bad or isn't properly seated it can cause issues like this. My rear hatch will open only with the key fob BUT I have purchased a new touchpad through RockAuto.com and just need to install it. I know that there is a lot of info about them going bad on the forums but you should check your fuses before you do anything. Some of the fuses are under the hood and some are inside the car and check your manual. There are diagrams that show what fuses are where so that will help you find them and check them. I haven't had any issues with my gas gauge but that could either be electrical or you might have a bad float that may need replaced. I am not sure what the technical name for it is but it is in your gas tank and measures how full it is. Hope this helps.

Check all body grounds