1998 Bravada. Noticed the other night I have no headlights. Here's what I've checked

The night time headlight socket both sides have 12v
The fuse box no blown fuses in both the under hood and dash side
I have extra relays from another Bravada I picked apart and replaced the DRL relays and anything that was headlamp related. No go.
The override switch inside does nothing
Brights don't work either.
I do have DRL lights
There is one strange fuse in the under hood panel has a diode symbol on it. I don't know how to test that.

Could definitely use some help. I don't know how different this system is than what run on the Blazers. I've tried searching, but nobody seemed to have this problem. Could it be the dash switch some how? I don't wanna go throwing parts at it. Waste of money.

 

I don't know if the wiring schematic is different from a 98 Blazer but I will assume not for the purpose of this issue. Before I can help I will need some clarification.

1. There are up to 6 lights involved up front: left high, left low, right high, right low, left fog and right fog. Which are you referring to when you say "nighttime" headlights?
2. Exactly which bulbs are on during the day with the DRL function?
3. So at night you have no lamp function at all from any of the 6 bulbs in either auto or manual on mode?

George

 

My DRL lights work and my fog lights work, but they are completely separate on a bravada. By night time I mean the main headlights that come on in low light conditions. I just remembered I was gonna go out and pull my switch out and take a look around again.

Update. I went back out and did a test with my power probe. I grounded one side of the night time headlight socket and the opposite side bulb would come one. I did it on both. So the bulbs are good, they just aren't getting grounded. I have no idea where to look after this point. I didn't look at the switch because it's doing exactly what it's supposed to as far as I can see.

What would happen if I spliced in a ground ?

 

I don't have any Bravada schematics and none of the Blazers use a separate set of bulbs for the DRL function so I don't know how helpful I can be. That said, I do understand wiring schematics. The 2000 ZR2 Blazer is the closest I can find and it came with a DRL function but not with separate bulbs, it just turns on the standard headlamp bulbs to perform the function. There is switching of both power and ground for all bulbs that involves the headlamp switch, relays, wiring and the BCM along with the ambient light sensor input. It sounds like you have power so that means that the dash headlight switch works, the power relay works and the relevant fuses and wiring are good.

The ground switching, at least on a blazer involves the multifunction switch and a "daytime running lamp relay" listed as "taped to body harness rear breakout for rear washer hose". So the lack of a ground for the headlamps can be these components, the wiring or the ground attachment point which in the case of the blazer is G117 right rear of engine. I would check the ground, see if you have that relay and the fuse for that relay is ignition E 10A in the UHFB.

Let me know what you find and we can go from there. Proper diagnosis depends on finding that relay and if that's good then accessing the MF switch harness. If you want to bypass all of this and are willing to lose some functionality then yes you can run a new ground wire to the lamp sockets but you would have to make sure that you don't have lights on when you leave the truck and you may lose switching to high beams and/or the DRL function.

We have a member here - Tom A. If you PM him he might be able to produce the headlamp circuit for your truck and if you send it to me or post it and then I can definitely help you. Another option is one of the online services, like DIY Mitchel1 or Alldata.


George

 

I have a friend's shop with alldata, I'll see if I can get some info from them. "taped to body harness rear breakout for rear washer hose" Any way to decipher that for me?

 

It looks like my Blazer schematics may get us in more trouble than help, we better wait until you get that Alldata schematic, then I can really help you on this. In the meantime I looked at your owners manual and the DRL relay may be in the UHFB:

George

 

Schematics are based off which bulb is used for DRL. Since most s-series trucks use the high beam in series for DRL (this includes the Bravada), any like year s-series will have the same headlight schematic with the exception of the ZR2 models which use the low beam bulbs as the DRL. THIS THREAD has schematics that you can review. I can't recall the source anymore as it has been a while since I pulled them.

 

Try this.

 

heck yeah thank you!!!!!!!!!!!

 

I contacted Tom and asked him to post the schematic for your truck. Are you good or do you need diagnostic help?

Thank you Tom.


George