Headlight switch does nothing!
 

I have a 99 Blazer and I would like to be able to turn off the headlights at night when the vehicle is running. When I turn the switch at night from auto to marker lights to on it does nothing. It will work at night with the vehicle off and I can turn on from DRL during the day. I tried the diodes in the DRL sensor, bending the relay tab back and pushing the dome override switch 4 times. None of this did anything. Do I have a bad switch or is this normal?

This is the automatic headlights working. In the dark, with the motor off and then started; the lights will stay off unless you turn them on manually. But as soon as you release the parking brake, they are in automatic mode and will come on. If you turn the engine back off. It will reset the system.

I'm working on a work-around for all this to be able to switch between the automatic headlight/DRL operation and full manual setting. It has taken me deep into the electrical schematics of the GM service manual to first understand the circuit. Then I've had to come up with a way to fool the BCM (the body control module) that the truck has never had the parking brake released or that it is dark out. My system will also disable the DRL system.

Just yesterday I placed my order for parts to do this which came to over $100. The heart of this is the intermittent switch (a fog-light switch from a Pontiac so that it will look stock) that will control a flip-flop relay that controls three relays in my circuit that will interrupt the signals going to the BCM. To do it right, I've had to get some nice, GM style connectors (although others would not have to go the same route) and tap into the circuit for the Retained Accessory Power (which is a whole other story but which I have already done to make an automatically switched power outlet).

I seriously considered dropping the project for all the headaches it has given me but it has now become a point of pride with me to see if I can do this. LOL

What if I just put a switch to ground the parking brake wire would that work?

Depends on what you want it to do.

Bypassing the park-brake ground switch will keep the Headlamp Ground and DRL relays from going into DRL mode but they will not disable the headlights coming on automatically. The parking lights would also still come automatically.

Below is the circuit diagram I created with my new circuit elements. The new relays and other components are in yellow. The rest is the original circuit. The new relays are in their off state so that the system is as if they were not there.

I have not tested this circuit yet so there are no guarantees it will work.

https://cimg4.ibsrv.net/gimg/blazerf...14f2f9cf6e.png

Push the dome light override button in and out 3 or 4 times and it will kick the lights off

this doesnt work on a 99

I'm working on a 99 now and it works on it

The one I'm working on is a 2000, my bad

I've seen this stated before and tried it on my 99 and I could not get this to work. I'd like some clarification.

Can someone who has made this work answer some detailed questions for me?

• What year is your Blazer?
• Does it have the automatic Daytime Running Lights DRL? (In addition to the auto headlights.)
• Does it have fog-lights?
• Does the headlight override only work once the automatic headlight system had already turned on the headlights?
• Does the headlight override also override the DRL system?
• What are the specific instructions for engaging this system?

I have a 2000 and a 2002. They both have automatic daytime running lights that are always on with the key. There are no special instructions on mine really. Anytime the key is on headlights are on, dohme light over ride button is located on the headlight switch. Push it several times and headlights go out. I have had 95 blazer, 96 s10 pickup and 98 pickup but didnt know of this method then, so I would push the park brake down just a hair to cut the lights off but not nearly enough for the brake to drag and never had a problem.