The bulbs are duel element. So, when the parking lights are on, one element is used in the bulb and when you turn the signals or brake lights on, the other element works. As far as the back up lights, that is a separate circuit and bulb system.
If you look at the first pic, I circled the two elements in each light. One is likely burned out in each bulb on the right side.
Here are directions for replacing the bulbs. The remaining pics correlate with the directions.
2006 Chevy Truck Equinox AWD V6-3.4L VIN F
Vehicle Lighting and Horns Brake Lamp Brake Light Bulb Service and Repair Procedures
TAIL LAMP ASSEMBLY AND /OR BACKUP, SIDEMARKER, STOP, TURN SIGNAL BULB REPLACEMENT
1. Remove the tail lamp bolt covers.
2. Remove the tail lamp bolts (3).
3. Pull outward at the front of the tail lamp assembly to disengage the retainers from the body side.
4. Remove the bulbs from the tail lamp assembly.
5. Remove the tail lamp assembly from the vehicle.
1. Position the tail lamp assembly to the vehicle.
2. Install the bulbs into the tail lamp assembly.
3. Push inward at the front of the tail lamp assembly to engage the retainers into the body side.
4. Install the tail lamp bolts (3).
NOTE: Refer to Fastener Notice in Service Precautions.
Tighten the tail lamp bolts to 2 N.M (18 lb in).
5. Install the tail lamp bolt covers (4).
From memory, I believe the bulb you need is a 2057. The last pic shows what it looks like. Take the old one with you to a parts store to get one if your's looks different.
I hope this helps. Let me know if you have questions and if this fixes the issues.
Images (Click to enlarge)
Tuesday, April 14th, 2020 AT 4:07 PM