Maybe a short. Can't check right now since it's raining, but judging from the diagrams, it does indeed appear that only one of the wires should be ground. If there is a black one, that should be the ground. LG/BK (light green with black stripe?) should be high beam power, and DB/WH (dark blue with white stripe?) should be the low beam power. Not sure if those are the colors leading to the harness pictures above, or if those are for the wires inside the headlight.

Either way, try to follow the wires coming from that harness down, and see if you can find a tear or break in there.

 

Will do, but in the meantime I checked the voltage and it reads 26.2 and 26 respectively with the headlights on.

 

Start with checking for power at the low beam fuses and the high beam fuse with the headlamps on.

If you have power on 1 side of the fuse slot for the headlamps, then the MFS is good.

26.2 volts ? bit high for a nominal 12 V DC system

Where did you take this reading at ?

 

I hosed it up, I apologize. The correct readings are 12.1 on both hots and -0.04 on the ground. The battery was reading 12.2V

 

Where did you take this reading at ?

 

Connectors 1 & 3 to the positive battery terminal with the headlights turned on.

 

Alright, went outside and took a couple readings.

First, I disconnected both connectors from the back of each headlight.



Using this picture and numbers as reference, here's what I got:

Passenger side:
1 = Black wire = Ground
2 = Dark green/orange = Low beams
3 = Light green/black = High beams

Driver's side:
1 = Black wire = Ground
2 = Dark blue/white = Low beams
3 = Light green/black = High beams
-----------------------------------
Headlight switch OFF
-----------
Continuity check with ground

Passenger side
1 = 001 ohms
2 = 1/ open, no sound
3 = 015 ohms

Driver side
1 = 000 ohms
2 = 1/ open, no sound
3 = 015 ohms
------------
Voltage check with the positive
-Voltage across battery = 12.31V

Passenger side
1 = 12.31V
2 = 11.65V
3 = 12.31V

Driver side
1 = 12.30V
2 = 11.65V
3 = 12.30V
-------------------------------------------
-------------------------------------------
Headlight switch ON, low beams
Continuity with ground

Passenger side
1 = -006 ohms
2 = -580 ohms
3 = -34 ohms

Driver side
1 = 006 ohms
2 = 1,open/ no sound
3 = 61 ohms
--------------

Voltage with positive
Voltage across battery = 12.07V

Passenger side
1 = 12.07V
2 = 0V
3 = 12.01V

Driver side
1 = 12.06V
2 = 0V
3 = 12.01V
--------------------------------------
--------------------------------------
Headlight switch ON, high beams

Voltage with positive

Passenger side
1 = 12.05V
2 = 0.01V
3 = 0.01V

Driver side
1 = 12.05V
2 = 0.01V
3 = 0.01V
-----------------------------------------


All these readings were take at the harness. Also, have your tried swapping headlights? The connector seems to be oriented the same for both sides. Who knows, you might have a faulty ground within the headlight.

 

#2 was the black wire on mine and ground IIRC. It read 0V. I have not looked at the headlamp assembly yet, though it is plan A in the morning. I was told that since I ran a voltage check from the #2 to pos terminal on the battery and it was 0V then the issue was with the ground in the harness.

 

You want to test from the low beam pin to the ground pin ( on the headlamp connector ) with the headlamps on.
Next push the MFS forward, and test the high beam pin to the ground pin. Both should show 12 V + DC.
If both are 0 V, then use a ground lug or the neg side for the low and high beam pins.

Not sure what testing to the + side of the battery is trying to prove, that not how this should be tested.

When doing the test at the headlamp housing connector, you are testing towards the truck side of the harness ?

The other quick test, is if those pin assignments are correct, you can jumper power to the low beam pin, and ground to the ground pin ( towards the headlamp housing ) and the lights should work.

 

I will go try it again like you suggested, but I'm not sure how jumping the connectors will make the lights work since I have the harness unplugged. BTW Thanks for the help, it is MUCH appreciated!

 

If you apply +12 VDC & ground directly to the side of the harness the bulbs are on, they will light. This is what the truck normally does when you turn on the main headlamp switch. This is testing from the connector to the bulbs.

 

I just tested the passengers side and only the passengers side. I am still new to multimeters so please bear with me.

I've added my results to the right of yours and in bold italics.

 

Do as SSCULLY suggests. Also, try swapping the headlights. I would essentially be doing what SSCULLY is telling you, since you know the drivers side works, and the plug layouts are the same.

 

Swapped the headlight assemblies and are more confused. The DS headlamp in the PS works fine. Turned on the lights and BAM the low beams were on. Flipped on the high beams and both lamps were on.

I could NOT get the low beam to come on on the PS headlight assembly, even after changing bulbs to make sure it wasn't a bad bulb. Is it repairable or do I need a new assembly?

 

Time to meter from the square connector to the bulb connectors.

Check ground to both bulb holders and the lo & high beam to each bulb holder.