2004 buick rrendezvous anti lock brake and traction lights stay on.

That means there is a problem with the ABS , has DTC'S - diagnostic trouble codes in the EBCM - electronic brake control module . You need to have diagnostics run on it !
Traction Control/ Stabilitrak Off: Refer to ABS Description and Operation in Antilock Brake Systems
This vehicle is equipped with the BOSCH 5.3 antilock braking system.
The vehicle is equipped with the following braking systems:
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Antilock Brake System (ABS)

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Dynamic Rear Proportioning (DRP)

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Traction Control System (ETS) (w/NW7)

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Traction Control System (TCS) (w/NW9)

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Vehicle stability enhancement system (VSES)

Bad abs sensors.

Your anti lock brake light is part of your traction contol lights so that is most likely a wheel sensor and would be a separate problem from your check engine light.
Do you have an auto parts store near by? They can check these codes for free if so

You will need to take it to the GM dealer or any well equipped brake shop and have the system ABS/Traction Control system computer scanned, a fault has occurred in the system and at this time you have no Traction control or Anti-Lock brakes. When the lights were turned on the systems control module stored a code for the fault in the system. The ABS and Traction Control are one in the same system.

Abs Light:
If its glowing momentarily while driving in slick conditions then its normal operation..
But if it stays glowing even under dry pavement then there is a problem with your anti lock brake and traction control system..
It happens commonly of wheel speed sensor which malfunctions..
Try to access the data in the anti lock brake module to find out which one malfunctions..

check to make sure that all the the bulbs in the rear are working,even the third light

Sounds like you have a problem in the front brakes or a front wheel speed sensor. A common cause for a Traction light is a faulty front ABS wheel speed sensor or harness. When the Anti lock brake computer sees a problem in the ABS syetm, it disables traction control as well.

The traction control system is controlled through the Anti-lock brake system. The way it works is if one of your wheels starts spinning the ABS applys the brake to that wheel to transfer power to the oppsite wheel that is getting traction. If your ABS is bad then your Traction control won't work. To check it I would find a parking lot on a wet day. In an open space mash in the gas. if you hear the ABS system kick in and you don't squall the tires then your good. My guess is you won't. What I would be worried about is will my ABS work. When checking the traction control is a good time to check the ABS. Acclerate to around 15 mph, then mash the brake as your live depended on it. If you hear a motor run and feel a vibration or grind in the brake peddal, then it works.

wont do it any harm,but you wont have a.b.s either best to sort it out its a safety issue

I own the 2002 Buick Rendezvous CX and I've encountered the same problems listed here. The ABS / Traction Control Lamp stays on and was throwing a code for the left wheel speed sensor as well as an anti-lock brake code (both in the wheel bearing hub assembly). I replaced the left and right front wheel hub assembly yet this did not eliminate the abs codes. 
Ultimately, I traced this problem to a break in the wire that leads to the left hub assembly. Although the sensor was properly connected, the wire (which is encased in a plastic housing) was broken. This is the wiring which leads from the abs wiring harness under the hood down to the left wheel abs sensor. 
I would suggest that you simply remove the left wheel and inspect the wire that leads to the abs sensor (there is only one wire on each wheel). Mine literally fell apart when I removed the plastic housing around the wire. I spliced the wire together and put it back in the plastic housing. After this, my abs codes disappeared and my anti-lock brakes began working again!
This is a simple fix that many people spend $1000 + on by replacing the hub assembly which does not fix the problem.