Drivers side headlights hi and low is out!?

Blackblu02 · May 17, 2017

My drivers side headlight does not turn on. I switched out bulbs, and checked connections and all check out. Next step was to check fuses and relay. My truck has two fuses, one for each headlight. They looked ok. Relay clicked when I turned on the lights so that's good also. I then pulled out my meter to check that I am getting voltage. Checked passenger side fuse and I have 11.9V. Checked drivers side fuse and my meter bounces around. It goes low and hi, but not the steady 11.9 from passenger side. I then took fusebox off to check bottom connectors, all look ok. I am now out of ideas. I ask you fine folks for any advice on this issue or maybe something I missed. I appreciate all feedback. Thanks!

newdude · May 17, 2017

Do you have power at each bulb connector itself?

Blackblu02 · May 17, 2017

Power only to passenger side headlights. No power going thru drivers side. I checked voltage at drivers side fuse, and I have NONE. That's why I'm a little confused. Correct me if I'm wrong, but the fuse box is like a distributor of power to various components right?

Blackblu02 · May 17, 2017

Do you have power at each bulb connector itself?

This is how I think it goes and correct me if I'm wrong:

BATT-->ECU-->Fuse box-->headlights. Of course the other components such as dimmer switch and hi low switch on column are also wired in, but that's what I think the gist of it is. Let me know if I'm missing something. Thanks!

newdude · May 17, 2017

I'm wondering if you have a power output problem after the fuse, or between the fuse block and the forward lamp harness for the left side. Bad wire, broken wire, corroded wire or there is an internal fault of the fuse box which has happened before and even happens on newer trucks (2007-2016).

Blackblu02 · May 17, 2017

I'm wondering if you have a power output problem after the fuse, or between the fuse block and the forward lamp harness for the left side. Bad wire, broken wire, corroded wire or there is an internal fault of the fuse box which has happened before and even happens on newer trucks (2007-2016).

Yea I'm thinking that I have no power output from fuse. And I'm trying to figure out where THAT power comes from so I can troubleshoot it. Thanks for your replies??

Heavy 5.7 · May 17, 2017

Relay clicked when I turned on the lights so that's good also.

Not necessarily.

newdude · May 17, 2017

Yea I'm thinking that I have no power output from fuse. And I'm trying to figure out where THAT power comes from so I can troubleshoot it. Thanks for your replies

Relay is first in line then the fuses. I'm betting that any wiring from the relay to each fuse is something part of the fuse block.

The engine wiring harness junction block supplies battery positive voltage to the normally open headlamp relay switch circuit. The TBC 10 A fuse in the engine wiring harness junction block supplies battery positive voltage to the headlight and dimmer switch assembly. The body control module (BCM) also supplies battery positive voltage to the headlamp relay coil circuit for automatic headlight control. The coil circuit of the headlamp relay is then grounded at G102. When the driver places the headlamp switch in the HEADLAMP position, the headlamp relay is energized. Depending on the position of the dimmer switch, the current flow is to both the left and right headlamp fuse, and to either the low or high beam headlamps. From the dimmer switch, the current flow is to ground at G203. The TCB 10 A fuse in the engine wiring harness junction block supplies battery positive voltage to the headlight and dimmer switch assembly flash to pass switch. When the headlamp dimmer switch handle is pulled toward the driver, both flash-to-pass switches close, one grounding the high beam circuit at G203. A second flash to pass switch also closes providing battery positive voltage to the BCM flash-to-pass input. With the headlights in the low beam position, the high beams may be momentarily turned on or flashed with the dimmer switch handle.