Headlight Help

[dmuldrew]

Ive got a 91 998 that I finally liberated from my buddy's body shop. All of the marker lights and turn signals work. The headlights do not come on. Any suggestions where to start?

 

[kendelrio]

Check the dimmer switch. Bad grounds can cause that, or you may be in "bright" and that sidefof the relay failed.

Please keep us informed.

PS... that is a BEAUTIFUL truck!

 

[dmuldrew]

Check the dimmer switch. Bad grounds can cause that, or you may be in "bright" and that sidefof the relay failed.

Please keep us informed.

PS... that is a BEAUTIFUL truck!

Bad ground where, battery, lights, body? not much of a wrench turner but I can sure replace parts! BTW they have worked in the past.

 

[kendelrio]

Bad ground where, battery, lights, body? not much of a wrench turner but I can sure replace parts! BTW they have worked in the past.

Things fail over time... it happens.

Silly as it sounds, have you turned the headlights on and switched from bright to dim/vice versa? That's the easiest way to check the dimmer switch, and I have spent hours in my youth troubleshooting lights and that was the issue. In fact, there is this thread where a young man went through DAYS of tracing wires, connections etc on his deuce and it turns out it was his dimmer switch..... and his trouble was identical to yours.

Try applying the advice in that thread to your Hummer and see if that helps. (Start with the dimmer switch, that was that young man's issue).

Please keep us updated.

 

[kendelrio]

Oh, and "replacing parts" is an EXTREMELY expensive way to troubleshoot.

Learning your tools and vehicle will save you so much money and it really does give you peace of mind knowing your vehicle electrically and mechanically.

If you have any questions about electrical troubleshooting (how to use a meter etc) feel free to PM me. We all have to learn somewhere and it's always best to ask and learn before tearing something up.

 

[dmuldrew]

Things fail over time... it happens.

Silly as it sounds, have you turned the headlights on and switched from bright to dim/vice versa? That's the easiest way to check the dimmer switch, and I have spent hours in my youth troubleshooting lights and that was the issue. In fact, there is this thread where a young man went through DAYS of tracing wires, connections etc on his deuce and it turns out it was his dimmer switch..... and his trouble was identical to yours.

Try applying the advice in that thread to your Hummer and see if that helps. (Start with the dimmer switch, that was that young man's issue).

Please keep us updated.

Yeah I tried bright and dim both and nothing. Dimmer switch looks easy to replace. I'll read over that thread. Thanks

 

[dmuldrew]

Oh, and "replacing parts" is an EXTREMELY expensive way to troubleshoot.

Learning your tools and vehicle will save you so much money and it really does give you piece of mind knowing your vehicle electrically and mechanically.

If you have any questions about electrical troubleshooting (how to use a meter etc) feel free to PM me. We all have to learn somewhere and it's always best to ask and learn before tearing something up.

Yeah I have no idea how to use a multimeter. I believe I have one my brother gave me when he upgraded, he failed to school me on its use

 

[papakb]

Once again, the internet is your friend:

 

[BLK HMMWV]

Technical manual section.
Light switch
I'm guessing/ hoping you actually have the switch in the right position.
Open the hood and see if the wiring harness is connected.
Perhaps your buddy removed the hood and forgot to hook the head light wiring harness back up?

 

[kendelrio]

Technical manual section.
Light switch
I'm guessing/ hoping you actually have the switch in the right position.
Open the hood and see if the wiring harness is connected.
Perhaps your buddy removed the hood and forgot to hook the head light wiring harness back up?

Good call! One of the things I was first taught was "What was the last thing touched?". Very possible the lights weren't plugged back in!

 

[dmuldrew]

Once again, the internet is your friend:

 

[dmuldrew]

Not much progress today, back to work. I did look over the headlight harness, and yes they are attached. Altho the ends of the wires that connect to the lights are in horrible shape. Can those ends be bought? Any suggestions how to deal with this issue.

Ive decided the first thing I will do in this great adventure is instal a ground harness. I'll see what happens, and proceed from there. Stay tuned.....

 

[Coug]

Not much progress today, back to work. I did look over the headlight harness, and yes they are attached. Altho the ends of the wires that connect to the lights are in horrible shape. Can those ends be bought? Any suggestions how to deal with this issue.

Ive decided the first thing I will do in this great adventure is instal a ground harness. I'll see what happens, and proceed from there. Stay tuned.....

If the ground harness seems to fix the issue for you, that means you really need to go through the truck and clean up all your ground points.
It's there to help, not replace, the original ground connections.

 

[Milcommoguy]

What's with the magic of the ground harrness? It left the factory without one and all was OK. One would think that if along the way it was missed / discovered or needed one, an MWO would have been issued. yes / no ???

Here's an idea... Get out the TM and take a peek at the electrical drawings.

At first look ...a maze and trying to find "Waldo" fun. Find the item of interest. "HEADLIGHT" (last week was a starter... tomorrow??)

Follow the lines / wires from headlight (left or right) to where they go. Each is labeled with a number. 91x (not 19) is ground. Note it goes to all the lights in the hood thru the connector and ties into 79x and then to body ground. This is easy to check. Ohm meter to either lamp 91 to frame and read something +/- 1 ohm as in a short to the frame GROUND. Test meter to be sure first.

Mulitmeter selected to DC Volts greater than 30 Volts, black lead to a known frame ground. Red lead is the testing lead. Get ready after studying print.

Headlamp # 17x is Hi beam...#18 xis LO beam. Follow them back to Hi/LO selector switch. Visualize how the simple switch works. It selects HI #17 or LO #18. The power feed is 16x from the lighting switch connector "M". Must have 24 Volt with lighting switch in "SER DRIVE" position and not in PARK feeding lead 16x to the dimmer selector switch. MAKE SURE the leads are in the right places on the switch too.

Lighting switch power feed is on its connector "F" It is present at ALL times... unless the "Start Box' is toast or a BIGGER problem.

So... the clue to finding "Waldo" is work it with what we now know ... forwards & HOT.

With the red lead from the handy dandy multi-meter. 24 Volts at lighting connector "pin F" ? YES, Replace connector and move on to HI-LO selector pin 16x and position lighting switch to proper position above. 24 Volts ? YES connect it all up and check #17 and #18 at head lamp buckets. Select HI then LO and see if voltage follows, Yes ...... connect lights works Yes... NO, Bulbs likely burned out.

OR ... any NO condition requires digging in to where the first NO occurred.

Note. Lighting switch, dimmer switch, connectors, pins, plugs, wires... if you can think it... could be bad. Keep alert to all the bits and pieces.

Go for the "YESes" and move forward. " NO's" check again and back up... with the thinking cap on, CAMO

I'am not sure this helps?? Was fun writing. I would like to think it does. "Waldo" can be found... LOL. This logic (more or less) as served me well on HumV. YRMV GOOD LUCK !!!

 

[dmuldrew]

LOL, clearly some of you have a great deal of experience dealing with these issues. Me, I go to work every day and give a calculated dose of poison to my sick patients to make them unconscious. Then I keep em alive so surgeons can do what they do. Then I wake em up. Frankly to me its childs play compared to looking at a wiring diagram. Its a foreign language I cant read, speak, or understand. But slowly I will get it. I do appreciate the skill and experience you all have, and the wisdom you are willing to share with the rest of us.

 

[TOBASH]

I will add a few things here. First, did you check the lightbulbs themselves to make sure that they are both working and not blown?

Did you check your light switch to make sure it is not in a mode where the lights are dimmed or the lights are out for stealthy driving?

Did you ensure that after all that body work the lights were plugged back in?

Reading and troubleshooting a TM is no different than figuring out an ATLS pathway. It is no harder than a brachial plexus pathway question in first year medical school anatomy dissection, or second year neurology. If you can pass gas you can figure this out.

IMHO

 

[papakb]

I'll admit that passing gas and reading schematics are two different worlds but if you mastered one of them you should be able to handle the other. There's some good videos on You Tube about using a multimeter and troubleshooting stuff.

Have you considered the fact that both headlights may have taken a power surge and both are blown out? With your multimeter on the low range resistance scale with the headlights unplugged read between pina 17 and 91 and then between 18 and 91. This will check to see if the lamps themselves are still good if you get a low resistance reading.

BTW, for HMMWV stuff a simple meter will work fine. You don't need a $300 Fluke meter to make these readings. Home Depot has Klein or Greenlee meters that will work just fine.

 

[dmuldrew]

I haven't really checked anything. I just got possession of it after spending some time in my buddys body shop. He lost his help and was all alone during the Covid thing, so everything was slow. The wiring harness to the headlights is connected. I have had the switch in the correct position. They did work when I first got it. I'll dig out the multimeter my brother gave me and try to make some progress this week. Where will I find TMs with wiring diagrams, trouble shooting and maintenance details?

 

[jkcondrey]

TM'S are located at top of the main screen, under "present conflict vehicles", then go to page last page of items and it will list m998, click that and there will be a multitude of pdf's to open. Some are operator based, maintenance based and parts based.

 

[dmuldrew]

TM'S are located at top of the main screen, under "present conflict vehicles", then go to page last page of items and it will list m998, click that and there will be a multitude of pdf's to open. Some are operator based, maintenance based and parts based.

Thank you very much!