Hi All,
I'm hoping someone can give me more options on this issue. My drivers side headlight went out just on the low beam, high beam, running lights and blinker still work. Every once in a while the low beam would come back on then go off a few days later and changing the bulbs didn't do anything to fix it. We've replaced the fuse (small red one) and the HDM (big black one) with no luck. We then decided since it must be a socket, connector or wire we'd just replace both headlight assemblies and go from there (they were dull from years of driving so needed it anyway).
The 4 wire pigtail from the harness has one pin giving no reading whatsoever - the second from the left yellow or white. Is this the ground? And, is there a schematic I can look at that will say specifically which fuse this wire goes to so I can just start there and replace the entire length back down to the pigtail??
I've tried going through the online schematics, researching and looking for videos, but I'm lost on this one. Once it gets to the fuse box there are a number of wires the same color and I don't want to pull something else loose. The auto store says they cant help me because the headlight only takes a 2 pin connector even though the original headlight and the new one both take the 4 pin.
Any help would be greatly appreciated. Thank you in advance!

 

First things first. What make. model, engine and year is the vehicle you are wishing assistance with?

 

I am so sorry! I re-read that like 40 times and missed that I didn't include it!
2002 Chevy Trailblazer

Someone told me today it was possibly the turn signal?
Thanks!

 

Thanks for the information. I've attached 2 schematics - one for the headlights, and one for the headlight switch.

I'm not sure which fuse the "small red one is for", and I am going to guess that the big black one (HDM) you refer to is the Daytime Running Lights relay.

First, if the multifunction turn signal switch/stalk was involved, then I think it would show up in the high beams not working right.

I think you can also rule out the Daylight Running Lights Relay because if it were flaky, then it would more than likely effect both low beams.

OK, here is what I think is going on - you have a bad electrical connection somewhere in the system. Most likely the problem is either a bad ground wire connection or one of the bulb sockets is defective. OK on your need for a 4 pin connector as compared to needing a 2 pin connector. I believe you, and the best way to find what connector you need, is to go through the online ACDelco Pigtails/Sockets Catalog and search for a 4 pin connector that looks like the one on your wiring harness. You search by the number of cavities (in this case 4) and plug gender. When you find the plug you need, write down the part number and then go to the Standard Motor Products (SMP) and BWD online catalogs and put the ACDelco Part Number into the cross reference field and get the SMP and BWD part numbers and use those part numbers at your local auto parts store (I would go with O'Reilly or NAPA) in order to get the connector.

ACDelco Pigtails/Sockets Catalog website: ACDelco Catalogs

Standard Motor Products Catalog Website: https://www.standardbrand.com/en/ecatalog

BWD Online Catalog Website: https://ecatalog.smpcorp.com/bwd/#/vehicles

OK, I've also attached a line drawing of what should be one of your headlight assemblies along with the wiring harness that goes to it.

Now you need to know where a couple of grounds are, Ground G103 and Ground G107. Ground G107 is located on the driver's side of the engine block about midway back, and midway down. It is located right under the EVAP Purge Solenoid. See the attached picture, G107. Ground 103 is located on the passenger side engine compartment in what looks to be above the mid-point of the wheel well just below where the hood sits when it is closed.

Now, if you have a digital voltmeter (DMM), I would check for 12 VDC at the bulb sockets and work backwards. If you find that you do not have 12 VDC at the socket when you turn the headlights on, check the black wire and make sure it is grounded using the ohms function on the DMM. If you do not know how to use a DMM just let me know and I'll provide a quick instructional write-up.

I hope this helps. I know it's a little disjointed, so please forgive me.

Good Luck!