New Headlights Wiring issue - Need help

[Bill Davey MJLR]

My old M35A2 headlights are dead, so I decided to buy a cheap set of 24v LED headlights and adapters. The wiring on my truck is falling apart from age (brittle mostly) so it is possible I have some sort of wiring fault. However I get consistent, if not proper behavior from both head lights. There are only three wires on each headlight, so this should be simple to figure out, yet it is driving me mad. Out of the back of the light are three prongs, I got a diagram from the manufacturer that shows from top down with center pin up, left is ground, center is low beam and right is high beam. I have an adapter, with green/black going to ground, white to low beam and blue to high beam.
No matter the combination I attach the wires to the truck, I get strange results. Basically, if I connect green/black to ground and blue and white to the other two wires respectively, in one config, I get only high beams and the other I get only low beams in any switch configuration, however the high beam light on the dash does not come on at any point. Strangely if I change the blue to ground then I get the high beam light on the dash in any position. I am pulling my hair out. Should I just dump the LED's and find a std set of lights and give that try or am I missing something all together.



BTW the adapter manufacturer gave me this info for the wiring, however it is different than the headlight info I got (ref pic). "The blue wire of the plug is the ground wire. White wire is low beam and the black wire is high beam."

 

[Guyfang]

Do you have the schematic for this truck?

 

[ToddJK]

Head scratcher...
From the TM, it shows what wire is which. If it's hooked up correctly, still doesn't work and it did work normal before, either there's a bad wire, or the lights are not supported. I would make sure #17, 18, and 91 are in the correct plugs behind the bucket. 17 is high beam, 18 is low beam, and 91 is ground.

When looking into the light bucket from the front end, the left plug will be #17, high beams. The right side plug is #18, low beams. Bottom plug is #91, ground. If the plug does not match the prongs on the light, that could be a reason. Might have to make some wires with the plugs to go directly into the headlight bucket.

 

[Bill Davey MJLR]

Do you have the schematic for this truck?

Yes I do.

 

[Bill Davey MJLR]

Head scratcher...
From the TM, it shows what wire is which. If it's hooked up correctly, still doesn't work and it did work normal before, either there's a bad wire, or the lights are not supported. I would make sure #17, 18, and 91 are in the correct plugs behind the bucket. 17 is high beam, 18 is low beam, and 91 is ground.

When looking into the light bucket from the front end, the left plug will be #17, high beams. The right side plug is #18, low beams. Bottom plug is #91, ground. If the plug does not match the prongs on the light, that could be a reason. Might have to make some wires with the plugs to go directly into the headlight bucket.

Thank you for that. I have a feeling these lights will not work on this truck. I have ordered a set of the std OEM style lights and will try those.

 

[cattlerepairman]

I also used cheap LED head lights and made an adapter because I despise hacking into original wiring. I used a H4 female plug with pig tail to which I simply added Packard connectors. LED lamp plugs into H4 connecor, Packards plug into truck wire connections.
The wire numbers given above are correct; I wonder if your headlight high beam switch is defective.
Your led lights should work just fine.

Sent from my SM-G991W using Tapatalk

 

[GopherHill]

You can use headlights that use a separate bulb. 24v H4 bulbs are very available and much cheaper than seal beams. Check on Amazon and other places.

 

[Bill Davey MJLR]

I suspect a bad switch or wire is causing some issues. I have confirmed the wiring is correct and still not working properly. Once I get the stock lights next week, I will be able to tell for sure. rewiring the lights from the switch will be a pain. I wonder if anybody knows how to verify if the switch is problem or not?

 

[mgFray]

LED lighting requires a neutral (-) ground, with the positive being on the high/low beam. No idea how your vehicle is wired, but I've seen issues on other vehicles where the light is effectively wired 'backwards', a single positive and then the neutrals are switched. That won't work for most LEDs, but fine for bulbs.

 

[ToddJK]

Go to the TM section and download the TM # that is listed at the top in the picture. Page 212 is where it starts for lights and wipers. This should be a good place to start.

 

[Bill Davey MJLR]

Update - All is working fine now. Lights are installed and behaving properly. It turns out I had two problems, a short on the Low beam wire and a short in my brain. Both are fixed and so is the truck. Thanks all for the tips.

 

[ToddJK]

Update - All is working fine now. Lights are installed and behaving properly. It turns out I had two problems, a short on the Low beam wire and a short in my brain. Both are fixed and so is the truck. Thanks all for the tips.

Glad you figured it out and all is working properly. How do these LED headlights stack up to the original sealed beam headlights?

 

[Bill Davey MJLR]

Glad you figured it out and all is working properly. How do these LED headlights stack up to the original sealed beam headlights?

I mostly use this truck off road, I state that because these light are not DOT approved for on road. Now I do like how well they light up the road even the low beams are a nice clear white light and work pretty decently. The highs have a nice wide spread. On my old Deuce I had some Military LED's and they were great, these cheap ones are not quite as nice, but for the price, they do the trick.

 

[ToddJK]

I mostly use this truck off road, I state that because these light are not DOT approved for on road. Now I do like how well they light up the road even the low beams are a nice clear white light and work pretty decently. The highs have a nice wide spread. On my old Deuce I had some Military LED's and they were great, these cheap ones are not quite as nice, but for the price, they do the trick.

Okay. I wondered as I've seen those from time to time. I was gonna do the same and then I ended up adding some amber lights on the bumper instead but they work good for what I need. Maybe that will still be a conversion to make once my stock lights burn out.

 

[cattlerepairman]

Glad you found the fault!

 

[SGT. Renshaw]

Update - All is working fine now. Lights are installed and behaving properly. It turns out I had two problems, a short on the Low beam wire and a short in my brain. Both are fixed and so is the truck. Thanks all for the tips.

Where was the short? I'm having some issues with my lights. My high beams work but no low beam. Checked voltage low only has 16v and high has 24v. Been trying to figure out my issue before I replace my headlights.

 

[SGT. Renshaw]

Update - All is working fine now. Lights are installed and behaving properly. It turns out I had two problems, a short on the Low beam wire and a short in my brain. Both are fixed and so is the truck. Thanks all for the tips.