Passenger headlight inop but bulb and DC power present

[boomerdude]

I have a 2016 FR Georgetown 270s on a Ford Triton V10 chassis. Issue is the passenger headlight will not work. Drivers side works. Troubleshooting: took known good bulb out of driver side installed on passenger side. Did not work. Took passenger bulb and installed on driver side. It worked. Checked passenger and low beam fuses, all good. Changed headlight switch due to cover fell off and to possibly fix this issue. Bypassed ground wire at connector and wired to chassis, no change. Continuity checks good. power check at connector: 12.2VDC. Thought maybe connector maybe loose at connection and added dielectric grease for better connectivity, no change. Only thing I haven't replaced is the wiring and the light connector. (The connector because I can't find the replacement for it) ANY help would be GREATLY appreciated :0

[CA_Traveler]

Yikes - My 30 year old Fluke is missing a few modern features. 😞

But I like the terminology - ghost voltage - So much more understandable than this high impediance stuff that I learned about back in the day... :B

Now I want a ghost buster Fluke meter. :R

[Rick_Jay]

boomerdude,

Glad to hear you were able to solve the problem! 🙂

Also, kudos to you for posting your solution to your problem so that if someone else has a similar problem, your thread can help them diagnose their problem.

As a side note, if any of you are either Electricians or have a DMM which is designed for being used by Electricians, a common feature is a "Low-Z Voltage" function in addition to the normal voltage function. "Low-Z" means that it presents a much lower resistance when placed in a circuit to measure voltage. A typical DMM voltage input has an impedance (resistance) of about 10 million ohms! Meaning that when you put it across a 12V source, the current which flows is 1.2 MILLIONTHS of an ampere (1.2 micro-amps), from Ohm's Law. In most cases, this won't cause a noticeable voltage drop in other devices/connections on the circuit, so it appears to indicate that all of the voltage is there. Just like you observed.

But the "Low-Z" function usually has a resistance of just a few thousand ohms, meaning that the current which flows will be in the THOUSANDTHS of an amp range (probably around 4 milli-amps with a 12 Volt battery). This is over three thousand times as much current as on the Hi-Z voltage scale and will often indicate faults similar to what you observed. For electrical circuits, it's not uncommon for "phantom" or "ghost" voltages to sometime appear at a point in circuit. This could be due to parallel lines running next to each other, one powered, the other not. A variety of other reasons, but the point being, if you measure such a point with a normal DMM voltage input, it will indicate that a voltage is present. Put the meter on Lo-Z and the voltage usually "disappears", hence the "ghost" and "phantom" nomenclature. The added resistive load of the meter causes the voltage to be "dropped" by other components in the circuit, and thereby tells the technician that what they are measuring IS NOT a live voltage source. In your case, it would probably have shown something like 0-10 volts, depending upon the resistance of the corrosion at the connection. But it most likely would NOT show you the 12 volts the Hi-Z voltage scale shows.

Here's a Youtube video showing the Lo-Z function in operation on an AC circuit: How to Determine if a Voltage is real or a "ghost". (NOTE: on the second power strip, the ground has a fault (open) and is therefor NOT connected to true ground. That's why there is a "phantom" voltage showing up from ground to hot, instead of the expected 120V normally seen.)

And this is from Fluke's website on Dual Impedance Voltmeters.

Ok, probably way too much info, but maybe it was helpful for some of you techies!

~Rick

[boomerdude]

CA Traveller your right, need the 'load' to simulate real power usage...left that out in my troubleshooting history, good catch 🙂 Fis was debris/corrosion in up-stream connector. Thanks for your input!

[boomerdude]

Thank you all for such intuitive thoughts and advice...openspaces and wanderingaimlessly you were pretty close to the issue...Though I had run the wire harness from the connector to the back of the fuse housing and discovered the wire gauge changed (?!) Thought, well heck, there's a splice/connector in-between the fuse back and the low beam connector...somewhere....took two big harnesses apart and low and behold, a connector. Took it apart, shook the DEBRIS out of it, took a jewelers spike and cleaned the inside of the connector. Behold it works now! Thank you ALL for the fast response and God bless you all!

[CA_Traveler]

Sounds like you're making the classic mistake of measuring the voltage without the bulb in place. Voltmeters present a very small load vs a bulb. Insert a pin in the + wire near the bulb and measure with the bulb inserted. If not OK then you have a high impediance open upstream of the bulb. If OK insert a second pin in the ground wire and if it measures 0V then the connector is bad. If it's corrosion you should be able to clean it.

[Walaby]

Sounds like openspaces and wanderingaimlessly may be on the right track.

[wanderingaimles]

IF you have voltage showing at the socket both at the wire side, and the bulb side,,,,, try using a wire brush to get as deep in the socket as possible to clean the contacts. even try taking a small piece of crocus cloth, folding it and insert into the socket where the contacts are. A tiny bit of corrosion could be insulating your bulb.

[opnspaces]

I see you said that you can't find a connector. Maybe try pulling the bulb and see if it will plug into yours or a friend car. Then search for the socket for that year make and model of the car.

[opnspaces]

Unfortunately dielectric grease is not conductive. So adding the grease might have made the problem a bit worse.
One thing to be aware of is that it is possible to have 12.2 volts at the socket. But high resistance might stop any amperage from getting through. You might benefit from a 12 volt test light that will tell you if the current is enough to light a light. Amazon If the test light shows the socket good then either find a way to bend the prongs in the socket; Or just replace the socket, available online or at the parts house. Socket If the test light won't light then you're going to have to trace the harness and check for light at every connector you find. If it gets to be too much or too expensive you could always tap into the working light and run a power wire to the non functioning light. Harness

[BobsYourUncle]

:h
Hmmm....
Doesn't sound logical does it? What you have done for testing it is all good. Theoretically it should work. Especially if you have 12V and provided an alternate ground.

Does this system have the provision that many newer vehicles have for shutting off a headlight when you turn the signal light on?
If so, I wonder if its possible that has anything to do with it. Perhaps a malfunction in there....