All was working as expected when I installed LED headlights, now 2 set of 9004 in my 02 3500 5.9HO cummings. Now with LEDs, if I turn on factory fog lights, the high beams come on as well. Result is no low beams. Fog light go off when switch to high beams. So far have tries resistors and some special box which was to fix it. Special box keeps high off when lows on, but only have lows when high beam on. Reinstalling halogens returns headlights to normal operation when fog lights on. Looking at LEDs thru wwelding mask, it seems normal operation is to leave the low beam panel on when high beams come on. Any Ideas on how to convince the high beams to turn off when low beams are on?

 

The wiring for the LED light is probably wrong, it's so common with them being made in china

 

What kind/ brand? Bulbs, complete headlight assembly what?

 

Bulbs, the cheap kind. Just plug them in they should work. And do sorta.

 

To check this, just use test leads and 12V, follow wireing diagrams for bulb? any thing else I should check?

 

You can I would make sure you are getting power on the low beam and high beam when you engage them and have a ground

 

Think its good, works fine with halogen bulbs, got low on low, high on high, no high on low with fog lites.

 

The cheap LED bulbs have crappy wiring where usually the high beam and low beam are reversed or something of that nature. That's why they are cheap.

Is your problem no fog lights?

 

Have fog lights, problem is high beams on when low beams selected and foglights on.

 

Do the low beams come on when your select high beams?