Drivings lights dont work on 99 tahoe

Hello, on my 1999 Tahoe my driving lights recently stopped working.. the green light is on but my lights arent.. Are they only supposed to come on when its in gear? i know on the 2000 and newer ones its set up like that but I'm not sure about the 99's..its the older style so it was the low beams that are the day time running lights... They used to always be on as soon didnt matter if you were in park or not like it does on the new style Tahoes.. not sure if it was already malfunctioned or not.. can someone fill me in if they are always supposed to be on when the key is turned on or are they supposed to come on when i put it in gear? Thanks for any info... but my problem right now is that they dont work at all.. my green light on the dash comes on when i turn the key on and start it but no lights..I checked the fuse and its fine and looked fora relay in the fuse box under the hood but i didnt find one...is there another place i didnt check? any info would be great

Thanks

do the vehicle have an ambient light sensor?(little black ball on the dash)...may be the culprit or a bad ground