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How to fix my 2004 Grand Marquis

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2004 grand marquis LCM already replaced under recall :()
Hello Scotty we have a 2004 Grand Marquis with 150,000 miles. The LCM light module was recalled several years ago and was fixed by another owner but now the back lights are not coming on (the running lights come on) do you think the LCM would go out AGAIN?? also, how often are you supposed to change the plugs and wires? We live in Augusta, GA
 
Edit: no the running lights in the back don't come on (but the break lights and other running lights do work fine)
 
 
This topic was modified 2 weeks ago 2 times by markmat

Do the running lights in the front work fine? Or do both front & back running lights not work?

only the running lights in the back don't come on.. but the front is okay.. we took it to a great mechanic here in town and he fiddled around with it and said it's on now but it probably will go back out.. and so they did work properly for a day or so but then they went back out and won't come on at night any more.. but I don't know what he did to make those back lights work for that short time.. but he did say it was probably the lighting control module - they checked the fuse and there is nothing wrong with the fuse 

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The way you could test this is by bypassing the LCM and seeing if the tail lights illuminate.

The connectors on the back of the LCM look like this.

The White connector on top is called C2145b. I added some text to show the tail light circuit.

Here's the pinout of the C2145b connection ON The LCM.

 

The pinout says that power to the tail lights comes into the LCM on circuit 195 (TN/WH wire) on pin 12. When the tail light relay inside of the LCM is energized power goes out on circuit 14 (BN wire) from pin 4 to the tail lights.

The wiring connector side is the mirror image.  So those  pins on the connector look like this.

 

To troubleshoot if this is either a power/wiring issue to the tail lights or a faulty LCM you can just disconnect LCM connector C2145b and use a paperclip to jump the (connector side) 3rd pin from the right on top with the 5th pin from the right on bottom.

If the tail lights illuminate then it's likely a faulty LCM.

 If the tail lights don't illuminate then it isn't the LCM. It's either the light switch or the power feed (to pin 12) or the wiring to the tail lights from pin 4.

 

well I was looking at video about a burned out component in the LCM.. if something is BROKE in the LCM then nothing but replacing that will cause the lights to come on again.. HOWEVER they did something to the car and the lights came back on for a couple days and then they went back out again.. so can I deduce that it isn't the LCM from just that?

I read your reply to itwt on how your mechanic was able to get those lights to work again but cautioned you that the LCM would probably need to be replaced
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If you watched some videos on those you've seen that the common reason they fail is either broken solder joints or a failing relay (one of those 4 square boxes on the circuit board)
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Frankly I think your mechanic was able to get the lights to work again by smacking the LCM a couple of times which sometimes works with broken solder joints and sticky relays on a circuit board (but it's always just a temporary "fix" and he warned you that it would be)
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(This also works for people with dash clusters with "cold solder joints") They can smack the top of the dash and their cluster works again (for a little while)
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When you pay a mechanic you expect him to test the circuit to rule out other possible issues with switches, wires, power/grounds, and light sockets before condemning the LCM
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That's why I suggested bypassing the LCM to test the rest of the tail light circuit and components and if those check out OK, it's a safe bet it's the LCM

thank you so much you are a sweet person God bless you we will fix it!

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