What makes my DTL just stop working?

on 1999 Chevrolet Tahoe

They just did not come on. The green headlight emblem comes on in the dash,
But the DTL do not come on. The regular headlights work fine. I changed the relay and the emergency brake switch but that was not the problem.

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2 answers 1 comment
did you ck bulbs?
Thanks for the reply. On the 99 Tahoe the DTL work with the headlights. There no seperate driving lights. The headlights work fine.
Any other ideas? Thanks again
Check ALL fuses?