2005 left front headlight (Low/High beam) not lighting

Hello, the left front low and high beam is not working. All other exterior lights work. Right side works. I pulled the headlight unit out and checked the 3 prong headlight bulb connector. The center contact has continuity to ground. The left and right contacts have 12.55V on them with the headlights off, when on 12.08V on high beam side and 12.08V pulsing to 12.48V on low beam side. The fog lights work when turned on.

So, what needs to be replaced or repaired. I have previously repaired the power module when none of the lights worked. Please help.

 

Using an ohmmeter to check for resistance with wiring and wiring connections is commonly used. Unfortunately, the test has no value. Example: A single strand of wire will pass a continuity test with flying colors, but that single strand of wire will not carry the current needed for the load.

A better test is performing a voltage drop test under a load if you can probe the connector terminals connected to the headlight while operating a known good headlight on low beam. Have the engine running and the low beam headlight switched on. Using a voltmeter, place black test lead on the ground post of the battery.

1. Place red test lead on the A terminal (low beam supply voltage) of the connector. Voltage should be 13 - 14 volts.

2. Place red test lead on the B terminal (ground circuit) of the connector. Voltage should be less than .2 volts

If there is no voltage or extremely low voltage in test #1, then the source of power needs to be checked.

If voltage on test #2 shows a significantly higher voltage than .2 volts, then there is a faulty ground.

The wiring diagram below is from a 2004 service manual, but I think the wiring is the same for a 2005 truck. Also, make sure there are no fuses in this circuit that could be blown. Second generation trucks had a fuse for each headlight.

- John



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John,

Thank you, it is a bad ground. I grounded the bulb's ground wire and the bulb lit, so it is a bad ground.
I could just splice into the ground wire at the plug but would rather fix it right. Do you know where the ground connection is located?

Len

 

Unfortunately, the service manual does not show G104 location, but I think you should be able to find it. You may have to remove the driver side battery to gain access.

- John

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Just above the light, left Hand, is the ground connection.

 

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On the 2004s there are a number of things that use the G104 ground location, including the left front park and turn lamps, and if you have them,the fog lamps. Since it seems that those are working, ohm out the headlight's ground wire between where you tested it and the G104 location, I'll bet that's where you'll find the problem.

 

I had a similar problem on my2005. One of the pins in the headlamp connector had backed out of the plastic housing and would only work intermittently.

 

Well Gentlemen, problem fixed. Somewhere between the High/Low bulb Socket's connector and GND is an open. I spiced into socket GND and a, previously installed, GND wire went from battery to The frame.
At least its nice outside.
Lastly, thank you all for your help.