Low Beam/DRL Interface
Thread Starter
CF Beginner
Joined: Jul 2018
Posts: 5
Likes: 0
From: Dawsonville, GA
Low Beam/DRL Interface
I have a 99 Suburban. I don't have an occasion to drive at night must so I was surprised to find my DRL's do not get brighter when I turn on the headlight switch. So, I presume I don't have low beams, or the low beams are not cancelling the DRL's if that's how they work. The other thing I noticed is i don't get a high beam inducator when I pull the dimmer switch up to flash the headlights with the headlight switch off. I presume it has this function. Or no?
High beams and the related indicator light work. DRL's and the indicator light work.
Where to start?
High beams and the related indicator light work. DRL's and the indicator light work.
Where to start?
Thread Starter
CF Beginner
Joined: Jul 2018
Posts: 5
Likes: 0
From: Dawsonville, GA
I figured this nutty DRL relay wiring out with a test light. Whoever designed this system must have been brain dead.
Relay pins 87a to 30 is the resting relay position. The headlight feed from the light switch goes through the relay in this resting position with the ignition off causing the headlights to burn standard. When the ignition is in run, the ignition switch sends power to pin 85 which switches the relay to pin 87 to 30 and causes the headlights to run DRL. With the headlight switch on, and the ignition in run, the DRL module it's supposed to chop ground or power (dont know which) to this relay causing the brighter light. I.e. A return to resting position. That is, the DRL's would therefore be disabled.
I fixed that goofy crap right quick. I cut off pin 85 of the relay and that disables the DRL system altogether by preventing power supplied by the ignition switch from entering the relay. The relay is now used only for the headlights, and it never clicks. Power just passes through it.
Everything is great. No DRL's to troubleshoot ever again.
I don't have fog lights so cannot say how they might be wired or fused.
Relay pins 87a to 30 is the resting relay position. The headlight feed from the light switch goes through the relay in this resting position with the ignition off causing the headlights to burn standard. When the ignition is in run, the ignition switch sends power to pin 85 which switches the relay to pin 87 to 30 and causes the headlights to run DRL. With the headlight switch on, and the ignition in run, the DRL module it's supposed to chop ground or power (dont know which) to this relay causing the brighter light. I.e. A return to resting position. That is, the DRL's would therefore be disabled.
I fixed that goofy crap right quick. I cut off pin 85 of the relay and that disables the DRL system altogether by preventing power supplied by the ignition switch from entering the relay. The relay is now used only for the headlights, and it never clicks. Power just passes through it.
Everything is great. No DRL's to troubleshoot ever again.
I don't have fog lights so cannot say how they might be wired or fused.
CF Monarch
Joined: Apr 2012
Posts: 6,216
Likes: 438
From: Miami, FL.
I had a 99 Silverado which should be the same DRL lights as yours and the DRL lights were not in the headlights. There is a light below the headlights which came on for the DRL. I had to replace the bulbs several times and the socket once because the heat melted the socket.
