My under dash lights stopped working on both sides.The upper cab lights still work.
What do you think it could be?

 

Pluck the low hanging fruit and work your way up the tree.

1. replace the bulbs
2. Crack open the fuse box. That should be your first reaction to any electrical problems.
3. Get a multimeter and wiring diagrams and start probing. Circuit troubleshooting is a vital skill with modern cars.

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