There isn't a dedicated daytime running light (DRL) relay in the traditional sense on a 1999 Chevy Suburban. The DRL function is usually controlled by the body control module (BCM) itself, which then uses existing circuits and relays for other functions to activate the lights. There's no single relay you can pinpoint as the "DRL relay."
To troubleshoot DRL issues on a 1999 Suburban, you need to diagnose the problem through the BCM and its programming, likely requiring a scan tool capable of reading codes and accessing the BCM's settings. A qualified mechanic or auto electrician with access to such tools will be best equipped to handle this.
