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turn signals and brake lights

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    turn signals and brake lights

    I've got an issue I hope this forum can help with.

    2005 Grand Marquis Limited
    Previous to this there have not been any electrical issues only normal maintenance items (AC blend door, tires, spark plugs, etc).

    The problem:
    None of the turn signals work (front or rear), the hazards do work (all the hazards lights work). The middle brake light works and the ones at the back don't work.

    What I've already checked or replaced:
    1. All the fuses under the dash are good.
    2. The brake switch at the brake pedal has been replaced.
    3. The turn signal stalk and stalk switch has been replaced (I think its called the MFS, multi-function switch).
    4. The LCM was replaced by the module in the recall (or TSB, I can't remember if it was a recall or a TSB)) before I bought the vehicle.

    Does anybody have any ideas of what to try next?


    You may have a bad relay in the lcm again. Take note, 2005 LCM is unique to 2005.
    If you open it up, there is a picture of an unknown year lcm at cvn
    Another picture with unverified labelling;

    The relays are conventional off the shelf 12 volt relays that you can buy from Mouser, Digikey, or whoever you prefer for electronic parts. The part number you find on them has been superceeded, but if you look at the part number on what you have, you can do the google hunt and find out what the replacement number is.

    To narrow things down, pop the cover off the lcm, put a finger on each relay, turn on and off the running lights feel which relay clicks, and then headlights to feel which relay does that (you'll have both the running and headlight relay clicking). turn the hazards on to feel which relay clicks, and the last one will be your turn signals. Give it a flick with your finger and try the turn signals again, if they work, you know you found your faulty relay without question. But relays are cheap, you either have 4 the same ones, or 3 the same ones with 1 slightly smaller relay.

    I'd also suggest using google to search cvn for external relay mod. You'll find tidbits of info scattered all over and some photos that still show up (aka: don't take everything for gospel that you read! it may not apply to the 2005) You do not need to do the external relay mod (just replace the existing relays in your lcm that need replacing), but those threads can give you some insight.


      Great info ^^^


        Also, check the connections for all of those things and make sure there's no bent pins and things are seated properly.

        Only two things are infinite, the universe and human stupidity, and I'm not sure about the former. -- Albert Einstein
        rides: 93 Crown Vic LX (The Red Velvet Cake), 2000 Crown Vic base model (Sandy), 2003 Expedition (the vacation beast)
        Originally posted by gadget73
        ... and it should all work like magic and unicorns and stuff.
        Originally posted by dmccaig
        Overhead, some poor bastards are flying in airplanes.


          Thanks for all this, I really appreciate it. I have a few more questions:
          1. This has the TSB for the LCM, is that TSB part different from a regular LCM?
          I ask because I thought I remembered the TSB replacement part being potted instead of being a PCB inside a box as the picture you linked to shows. I won't be able to confirm the potted part until tomorrow night.
          2. If it has the potted replacement part, Can I remove it and install the LCM from Rockauto to fix the issue?

          I'd like to replace whatever is currently there with this:

          Should that work?

          Thank you again, I really appreciate all your help and time on this,


            IIRC the the final lcm recall mounted some external relay for the headlights but did noting for all other lights. Could be wrong as I never had that done.
            03 Marauder DBP, HS, 6disk, Organizer Mods> LED's in & Out, M&Z rear control arms, Oil deflector, U-Haul Trans Pan, Blue Fuzzy Dice
            02 SL500 Silver Arrow
            08 TC Signature Limited, HID's Mods>235/55-17 Z rated Cooper Zeon RS3-A, Addco 1" rear Sway, Posi, Compustar Remote Start, floor liners, trunk organizer, Two part Sun Visors, B&M Trans drain Plug, Winter=05 Mustang GT rims, Nokian Hakkapeliitta R-2 235/55-17
            08 Escape Limited V6 Auto, Beamtech LED headlight bulbs,


              Thanks again for your help on this.
              I did have the recall, which is potted and you are correct it does add wires to accommodate what appears to be 2 external relays. I mistakenly thought it replaced the LCM, but it does not.
              I've ordered a new LCM off ebay (well, it's supposed to be new) and it should fix the issue.

              Also as a side note for anyone reading this in the future, for months the turn signals would flash quickly when turning in one direction and normal speed of flashing in the other direction even though all the bulbs were normal (no LEDS) and all were working. I think this is possibly the start of when the LCM was going bad.

              Thank you again
              Last edited by rollinns; 10-03-2022, 11:21 PM.


                Perhaps. But pull the tail lights out of the housings and visually check the individual bulbs for operation. You might be surprised how many people get caught by not noticing that one of the bulbs is not working when just looking through the lens. If everything is good back there, take a closer look at the front for one lone bulb that may not be up to snuff (aka pay close attention to the multi-filament bulbs as they might appear to be working but what you are seeing is the other filament lighting up dimly--gotta test them with headlights on and headlights off due to alternate ground paths)


                  Thanks for that tips to check the bulbs.
                  I replaced the LCM with the exact same part number, with a new one from ebay. Same result.

                  After checking the bulbs:
                  all the park lights work (they did before)
                  The flashers work on all for corners. (the correct filaments are lighting up, I checked each bulb)
                  No turn signals at all, front or rear.
                  No brake lights on the corners in the rear,
                  The center brake light still works (always did)
                  headlights work

                  New parts:
                  Brake switch at the pedal
                  Turn signal stalk and switch

                  The only thing that I know of that I've not replaced is the module for the headlights that was added when the TSB was done.

                  I'm thinking there may be a broken wire or terminal at the turn signal stalk, does anyone have a pinout of what wire does what function?

                  I bought a wiring diagram off ebay but it's for the year 2000, are the pinouts the same? (I'm suspecting not since the LCM is specific to model year 2005)

                  Also all bulbs are regular filament bulbs, no LEDS, it has never had LED bulbs.

                  Again all your help has been greatly appreciated and any further help is also appreciated.
                  Last edited by rollinns; 10-08-2022, 06:45 PM.


                    Considering you had that tsb done, key on, turn on a turn signal and start push-pulling every wire they cut and put a connector on. Might find a loose wire(s) and poorly crimped connectors.


                      I'll try that next. I put the original turn signal stalk (multi-function switch) back in and all the turn signals worked again. The upper third brake light works, but the corner brake lights till don't. I've ordered another turn signal stalk (multi-function switch) since the date code stamped on the turn signal stalk (multi-function switch) I got from said it was made on 4/15/14 (I'll probably call rockauto about this, as I've been buying from them for years and will continue to do so). I drilled out the rivets on the rockauto multi-function switch and used acetone to remove all the old grease thinking the grease dried out, then re-installed it but no change (still no turn signals front or rear).

                      That leads me to my final option (if replacing the multi-function switch doesn't work), what crown vic taillights (or maybe even towncar taillights) with separate turn signals will swap right onto my 2005 grand marquis?
                      I don't want to change the trunk lid or anything like that if at all possible. Maybe that question should be the start of a new thread.

                      The turn signals work, the third brake light works. So with crown vic taillights with separate turn signals, I'll run the current working turn signals to the crown vic turn signals and I'll pull the signal from the working third brake light to make the crown vic brake lights work, restoring all functionality and bypassing whatever issue is going on that I haven't been able to figure out.

                      Edit: it appears crown vic police interceptor or LX sport taillights will work fine with the wiring mod I mention above.
                      Last edited by rollinns; 10-16-2022, 02:14 PM.


                        On a vehicle with combined brake/turn lights, which this is, the multifunction switch is the place where the brake light circuits (but only for the left and right) get interrupted to allow the turn signals to flash. In a LCM car, the actual circuit make/break happens in the LCM, but it's possible a bad (or uncooperative) MFS could be telling the LCM to do that.

                        Since you've swapped the LCM, I doubt it's the LCM.
                        I'd say the same about the MFS but it's probably a more wear-sensitive part.

                        I'd try rapid-fire clicking the hazard button a few times and see what you get. The hazard function is the part of the switch that will simultaneously cut both the left and right lights.

                        Could also be something like a wire that isn't seated properly in its connector, at the MFS or LCM, but I don't know what those circuits look like to say for sure if that makes sense.

                        Current drivers: 84 TC | 85 CS
                        Panthers, Parked: 83 GM 2dr | 86 GM | 88 TC | 91 GM
                        Not Panthers: 85 Ranger | Ranger trailer | 05 Focus
                        RIP: 97 CV | 83 TC | 04 Focus | Junkyards


                          I finally fixed it, in the multi-fuction switch (MFS aka the turn signal stalk) I got a new one and it arrived damaged. I installed it and it worked the same way the Rock auto one did, meaning the turn signals didn't work at all, and still only the middle brake light worked.

                          The fix was that I first reinstalled the original Ford factory MFS. Then I started wiggling the wires on the top connector (top when the MFS is installed) and found if I pulled all the wires in that connector to the passenger side that everything worked.

                          I tried to pull individual wires but couldn't pinpoint which circuit caused the issue. Then I unplugged that top connector and used a dental pick to push on the bottom of each terminal in that connector so much that the bottom of each terminal was deformed inward so it would make constant contact with the corresponding pin on the MFS. I had to deform the terminals inward twice to get them to pinch the pin enough to make constant contact. That fixed the issue. I didn't even need to change the bulbs.

                          Maybe the LCM didn't need to be replaced, I don't know, it all works now and I'm not messing with it as I have needed this car to be operational for a while and I'm tired of working on it and have other projects to get to. I hope this helps someone who finds this in the future.

                          Thanks for everyone's help, I really appreciate it.


                            At least you figured it out. Hopefully that will provide enough contact and it won't overheat in there. I dislike connector fatigue.

                            Only two things are infinite, the universe and human stupidity, and I'm not sure about the former. -- Albert Einstein
                            rides: 93 Crown Vic LX (The Red Velvet Cake), 2000 Crown Vic base model (Sandy), 2003 Expedition (the vacation beast)
                            Originally posted by gadget73
                            ... and it should all work like magic and unicorns and stuff.
                            Originally posted by dmccaig
                            Overhead, some poor bastards are flying in airplanes.