If you have power on one side of the fuse socket, then the MFS is operating correctly ( MFS supplies power to cab fuse box # 26 & # 28 ).

The connector ( C159 & C160 ) for the cab fuse box to the front look like they both are either right behind ( towards the brake booster ) , or right under the engine bay fuse box, along the left fender.

C159 & C160 are both 40 pin square connectors. A square of 22 pin on the outer ring, and square of 18 pins on the inner ring, with what looks to be a center locating plug or bolt.

The 2 thoughts I have

1. By the headlamp connector, run part way up the low beam wire, and slice the insulation with a razor and check for power there ( looking for a bad socket )

2. Separate C159 & C160 and check for power there, then check for continuity from there to the headlamp connector.

The only other connector is C259 right on the cab fuse panel itself, which could be in question ( never say never ), but I would think other things would have issue aside from the low beams if this were the case.

 

Thanks SSCully - but thankfully it turned out to be simpler than that.

With some time and some daylight today I went back to basics. Long story short:

Both bulbs were bad
The spare bulb I used for testing was bad
My test probes were not making good contact on the lamp socket

Made up some better test leads, found 12 V on the socket, bought new bulbs, bingo back in business.

Moral of the story - don't try to fix stuff late at night, rushing, etc - and keep checking for the simple stuff!

Thanks again to all to helped - and as always I now know more about my truck!

 

Well i have a similar problem but one one of my lights dont work my passenger low beam doesn't work, ive already tested power to that connector only my high beam works, i dont have power to my low beam on the wire at all im not sure what to check now...

 

If you have the same model year range as this thread, the fuses up the page would be a good place to start from not having + VDC at the bulb connector.

Double check your owners manual, but fuse #26 is the passenger side low beam fuse.
- # 28 is the drivers side fuse

 

My auto lights work when it's dark outside. But my low beams are not working with my daytime lights. High beams work.
Any ideas

 

Can you complete your profile or post the information on your truck ?

 

when I bought this truck it was all blacked out. I'm wondering if the last owner cut a wire or something to disable the drl. The lowbeams work when the auto senser is covered or its dark outside. The mechanic told me all the fuses and relays are good. Mechanic seems to think my fuse box needs replaced 700$ and I don't believe that's the problem since the lights work on auto.

 

Did the truck have DRLs from the factory ?

Did your mechanic make sure that both DRLs relays and the DRL resistor were installed, or did he just look at what the truck had installed ?
- EG: the DRL was not installed.

There are 2 DRL relays ( DRL enable relay and DRL relay ) to make the function work, and the DRL resistor that is used for voltage drop to burn the bulbs at less than full brightness.
- This is in addition to the wiring needed for it, which may or may not be installed.

I only have the 2006 EVTM cell on DRL handy right now.





I would start with checking that the DRL relays are installed in the AUX fuse panel under the hood of the truck, before you go looking for the DRL resistor behind the driver's side ( ?) headlight

 

The problem that I had was that my passenger LO beam was very dim, like barely on. No problems on with the HI beams though. For me it was a very simple fix... turned on the LO beams, popped the hood and wiggled the bulb wires.

Apparently one of the three wires (I'm guessing their LO, HI, and Ground) was loose, the LO beam wire. No problems since...

Good luck!