One High-Beam is always on! '06 Town Car

[302w]

I would like to ask for help with two electrical issues that I am having:

1. I have an intermittent short in my parking lamp circuit. I keep blowing fuses.

2. This lead me to replace my passenger side high beam bulb as I was checking the headlight connector for corrosion. It is always on now! The old bulb was burnt out.

I tested the headlight socket and sure enough, Pin #1 (yellow/white) has 10v going to it with the key/engine off. I have no idea what could be causing this since the other headlight doesn't seem to have this issue.

I am hoping that repairing my high beam light fixes my parking light somehow, but I know that's just a wish.

Thank you!

 

[oktowncar]

Welcome aboard.

Check the RockAuto site. They have an assortment of connectors always available

 

[302w]

Welcome aboard.

Check the RockAuto site. They have an assortment of connectors always available

I'm not sure this would be the connector. There shouldn't be an "always hot" wire at the connector, as far as I know

 

[Action]

Not sure where pin#1 is located and power should be battery voltage. If your battery has 10 volts, then there is a battery issue too.
Otherwise, there is a wiring issue, and the connector may be the problem.
More diagnosis is necessary. Why only 10 volts? Why is the high beam powered up when the switch is on low beam only?

Action

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[etinpa]

I'd lean toward a stuck output on the LCM. You could unplug C2145C from the LCM to see if the issue is there or further downstream.

Wiring Diagram and C2145C drawing attached...

 

[302w]

Not sure where pin#1 is located and power should be battery voltage. If your battery has 10 volts, then there is a battery issue too.
Otherwise, there is a wiring issue, and the connector may be the problem.
More diagnosis is necessary. Why only 10 volts? Why is the high beam powered up when the switch is on low beam only?

Action

Battery is 12 volts and change with the engine off. The "always on" pin jumps to 12v with the high beam switch on.

I'd lean toward a stuck output on the LCM. You could unplug C2145C from the LCM to see if the issue is there or further downstream.

Wiring Diagram and C2145C drawing attached...

Thank you. I actually saw you helped someone else with a headlight connector issue, and your information there helped me diagnose this. So I appreciate your help already!

One thought I had... and this is beyond my skillset: how harmful would it be to cut the wire feeding the high-beam on my passenger side (the always on one), and jump it from the driver side (which acts normally)? Understanding the wiring between the LCM and the headlight is a little foreign to me.

Also, have you seen an LCM cause fuses to blow in the parking light circuit?

LCM replacements are a PITA requiring dealer programming, correct?

 

[etinpa]

Glad to hear you found some of my earlier posts useful!!

The fact that the 10V jumps to 12V with the high beams on makes me wonder about my LCM diagnosis... The voltage change means that the LCM output is actually controlling on & off. Makes me think the 10 V is coming from somewhere after the LCM. As I said before, I'd unplug C2145C from the LCM and see if the 10V goes away.

You could cut the power wire to the "always on" light and connect that light to get power from the working light but that would put the load of both high beam lamps onto a single LCM output which may or may not be able to handle the additional current. I would guess that could put the LCM at risk.

Also, if the 10V is coming from somewhere in the wiring harness or headlamp assembly it may be related to your other problem. I'd suggest troubleshooting properly.

 

[302w]

I'm pretty sure I pulled the right connector. The interior lights went out when I pulled it, and they're on the same connector.

Yes, the high beam is out with the connector pulled. Does this mean my LCM is bad?

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[etinpa]

I'm afraid the answer is YES. But, in this case a replacement of the LCM may not be required if you want to cut a few wires and rig a relay to bypass the bad output on the LCM.

A bit of detail on my thought process:

Ford may have three reasons that I can think of to use separate LCM outputs for the left and right hi beam lamps:

1. By using separate outputs for left and right, the outputs from the LCM could be rated lower and thus not able to handle the current of both lamps.
2. Separate outputs would result in loss of only one lamp is an LCM output failed.
3. Separate outputs makes police "wig-wag" lights a software rather than a hardware change in the Crown Vic police cars.

Because of #1, I wouldn't just connect the wire for the right headlamp to the output for the working left headlamp LCM output.
#2 likely isn't that important, especially for high beams.
#3 is irrelevant.

You could rig a relay so the coil is energized from the working left headlamp output of the LCM and the contacts of the relay bypass the bad LCM output getting power from the original source and supplying power to the right headlamp whenever the left high beam lamp is on. The coil would not add enough load to violate #1 above.

If you want a detailed description on how to do this, post back and I'll develop a drawing and instructions. In that post, please confirm that I have it correct that the problem is with the right high beam headlamp and the left high beam headlamp is working correctly.

 

[302w]

That was an awfully quick diagnosis!

In layman's terms, are you suggesting using a relay to energize the "bad" high beam bulb, using the "good" high beam circuit and power from, say, the battery? I thought about doing that.

My passenger high beam is always energized, driver is good.

Are LCMs plug-and-play? I saw a few threads stating that junkyard-swapped LCMs worked. I still have a mystery short in my parking lamp circuit, so my LCM might have another issue somewhere else, too.

In normal function, should the low beams go "off" when the high-beams are turned on? Mine stay on. I was wondering if anyone enabled "Bambi mode" with Forscan.

 

[etinpa]

In layman's terms, are you suggesting using a relay to energize the "bad" high beam bulb, using the "good" high beam circuit and power from, say, the battery? I thought about doing that.

Yes, the coil power would come from the working lamp LCM output while the contact power would come from the circuit that fed the original bad headlamp power into the LCM. That would keep all the factory fuse box markings correct.

I think LCMs are specific to the options installed rather than a specific VIN. Others may chime in to confirm or correct that.

I'm working from memory here but I think the low beams go off when the normal high beams come on but stay on when the high beams are turned on via "Flash to Pass".

I also don't know for sure if Bambi mode keeps the low beams on with the high beams or just keeps the fog lights on with the high beams. If the former, I'd have concerns about the heat of both bulbs on at the same time.