1999 GMC Yukon Daylight running light relay

The relay is located under the steering column. You have to take a panel just under the column to expose the relay that is plugged into a panel box. Good luck

If the Relay was not the problem you can check the Daytime running light module which is a circuit board (small) which the side of the card slides into a slot, that they tell is loacted taped to the panel or wring harness under the left side of dash. I have not found it but I know they sell this part both on-line and at auto part stores, so ut us there somewhere and could be your problem.

Most people do not mention this part, or do not know about it.

Good luck, gschall with 97 Yukon

Tony,
I found the daytime running light module however, that was not my problem, so I am moving onto checking the turn signal high beam switch, they tell me that can be the problem as well.
If I change it and it solves the problem I will let you know.

On my Yukon the relay is under the dash left hand corner next to the flasher relay. There is also a switch on the emergency peddle, (blue wire hot) that will turn the lights off if pressed so if that is bad no current flows with the brake OFF so test that for 10v or more with the key on first. Be sure to ground the other wire on the VOM and probe the plug on that switch with the plus probe. There is a diode under the dash also left of the steering column. The diode is probably the problem. Check fuse 15 and 4 in your fuse box first. If both sides of 15 are dead. The diode is bad. On mine I have do bend the 2 ears back on the bracket holding the diode and heat sink, slide it out and unplug it. Around $40 for a new one or a junk yard tested one will be less. Make sure the lights work on the car at the junk yard. Check out You Tube for your issue also. Videos will show you where everything is. It is one of 3 things. Emergency brake switch, relay or diode. You should see the diode under the dash in line with your radio on off switch straight down and under at that point. It has fins on it for the heat sink.

OOOPS>. The diode is RIGHT of the steering column, my mistake. Over under the dash behind where the radio on off switch would line up. Should be easy to see. The bracket is metal and has ears on it that can be folded back with needle nose pliers to slide the diode out instead of having to unscrew the whole bracket that holds it.