Hey guys, I've been constantly fixing stuff up on my 1999 Blazer LS and now both my driver-side headlights are gone.

I noticed a month ago that the hi-beam wasn't working, and then the low-beam stopped working about a week ago. DRL and turn lights are fine though. Right side lights are fine, possibly dim.

We spent the last few days trying to figure it out but to no avail. Bulbs aren't the problem, no power going to bulbs. Relay on fuse box is not the problem (put in new one anyway). 15A fuse for right lights gets power but 15A for left lights gets nothing (new fuses). We checked the electric light switch under the dash and didn't notice anything wrong. We opened up the fuse box and tried looking at the connections under the fuses, but didn't notice much. We cleaned a few ground ends, including two located under the air intake box by the lights, nothing.

No idea what the problem is, and the Haynes manual and google aren't much help. As of now, we are thinking its either the other end of the ground wire (not sure where that really goes or which ground is the right ground), or a fuse box problem. Buddy thinks a solution would be to splice the left and right lights together and use a bigger fuse, but I don't know about that.

Any ideas?

 

Well i will tell you this, you never just use a bigger fuse. Doing that will lead to melting and possibly fire. Now i will admit one of my first ideas for the fix to this problem, was a ground. By the tests you have done, you have narrowed it down to the headlight circuit only. No power to the bulb, no power to the fuse. I think it is a ground cable somewhere. My suggestion would be if you have a digital multimeter i would set it to do a continuity test. Pull the fuse from the side of the fuse block for the left lights. gently touch the contact for the fuse in the fuse block with the positive lead. then unplug the connector for each of your lights and insert the negative lead into the power side of the connector and see if the meter either beeps or gives you a reading. This means that that whole wire up there is complete and eliminates all that being a possible cause. Good Luck!

 

Do you know where the headlight grounds are? Specifically if, and where, there is a headlight relay ground wire. I have a feeling we may have missed one somewhere.

We did hit 4 grounds: one was on the side of the fuse box facing the lights. Second ground attached to one of the bolts for the air intake box (this one was disconnected, but reconnection made no difference). Other two were on the wall by lights, under the air intake box.

We couldn't find any useful diagram in the manual or on google for showing grounds. I'm having issues just finding a pic of a harness because it only wants to show me schematics lol.

 

Unfortunately I do not know where the ground is for the headlights but my guess would be somewhere on the radiator support or front fender

 

Since your right side lights are working, this suggests to me that both your headlamp power relay and headlamp ground relay are good to go as well as the multi-function switch. Since your DRL lights are working, this suggests that the ground in you Body Control Module is good. The only thing I see looking at the wiring diagram that is different between the right side headlamps and the left side head lamps it the left side shares power coming from the left side 10a fuze in the Underhood fuse block with the DRL Relay. So I would change out the DRL relay in the underhood fuse block (it's a five blade relay). There is a DRL diode also (little black thing that has a diode symbol on it) but I don't think that would cause the result you're experiencing. Assuming you have no opens in the circuit, it looks to me like that DRL relay would be your issue. Of course there's always possibility of corrosion in the wires, but if you are showing no power at all, to me it has to be that DRL relay or an open wire between the UBEC and your headlamp plug.

 

Sorry rockp2, I didn't see your reply.

I haven't yet figured out the problem. I plan to bring it to the shop tomorrow but I would really like to save money here.

I just realized today that my DRLs have been running all the time (night and day) on both sides. Shouldn't the auto DRL stay off at night?

One of the first things I did was put in a new headlamp relay. But I just read something about a second one. It's probably that DRL diode thing you mentioned. Where abouts is it located?

 

Sorry, it wasn't the DRL Relay that I changed but rather the headlamp relay. That definitely makes sense though considering what we saw when we pulled the fuse box apart lol. I'll definitely try changing that DRL Relay and see what happens.

 

Make sure you don't put the DRL relay in backwards. It may not be possible to, due to the openings in the UBEC. Don't have my Blazer in the garage right now, working on the Traiblazer. So, I can't give it a quick look to let you know. Just make sure you look closely at the old one when you pull it out and make sure the new one goes in the same way.

 

So funny story.

First thing I did today was go to the parts store. I pulled out that DRL relay and brought it to the clerk. They sold me a replacement relay, said it was the same kind of relay. So I went and plugged it in and nothing changed.

I took it straight to the shop. By the afternoon, they called me and told me that the problem was that the wrong DRL relay was installed. Turns out you were right and that was exactly the problem, but the stupid part store gave me the wrong replacement. Also, by coincidence, one of the bulbs on that side was burnt out, which only complicates things.

$200 later and it has adverted disaster again lol. That also includes tightening up all my leaking coolant hoses.

 

That sucks. If the guy had given you the right relay it would have been a $10 fix. But at least you're up and running again.