Where is the fuse for the brake lights for a 2003 buick lesabre

PWR WDO - 30amp circuit breaker , DRV -MDL 10amp fuse - both are located in the rear fuse box .
Fuse Block Rear
Under the left side of the rear passenger compartment seat

Step on brake pedal and see if you have brake lights. The brake light switch release the solenoid to let it shift. If brakes lights work then the solenoid could be defective. Also the fuses should be checked for the brake lights if they don't work.

Here is a great video on how to do that. It's also in your Owners Manual. Interior Fuse Box Location 2000 2005 Buick LeSabre 2003 Buick LeSabre...

To check motor mounts transmission in drive parking brake on accelerate lightly if a mount is worn the engine will raise up. also check in reverse.

On this website you find ruse box diagram and description for Buick LeSabre (2003)

Buick LeSabre 2003 2004 fuse box diagram CARKNOWLEDGE

On this website you find ruse box diagram and description for Buick LeSabre (2003) Buick LeSabre 2003 2004 fuse box diagram CARKNOWLEDGE

If it is like the 2002, one is in the engine compartment near the jumping post. The other is under the back seat.

check pully belt(fan belt ) and hydralic fuel.....

I hate to tell you this but its going to be a tough issue to find. You will need to check all the light bulbs are the correct bulb. Make sure they are correct not what was in there. I would check the brake switch on the brake pedal to make sure it is ok. then you will need to trace all the wires to find the short.

have you checked your fuses