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help with short diag-- wiring diagram for dome lights/clock/radio? general methods?

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    #1

    help with short diag-- wiring diagram for dome lights/clock/radio? general methods?

    OK so given a wiring diagram I can certainly figure out how to wire something up.

    But tracing faults... has never been a strong suit. And for better or worse I've never had the opportunity to practice.

    SO the other month several things stop working. My aftermarket radio has one of those automatically hiding faceplates, so a portion of it, the motor to pull it in, receives power even in key-off position. That stopped working. The dome lights and map lights no longer work. And the clock is off.

    On the fusebox by the steering column, fuse #8, a 15amp fuse, is blown. I replace it and all is well. The wires at the point of the fuse are green with a yellow stripe.
    Well it blew again a few days ago and it's a permanent short, now. Some wire some where is exposed and grounding...

    Does someone have a diagram? I can't find my book. May have lost it in the move 2 years ago. 1990 grand marquis.

    And any general advice for how to logically approach this problem, well short of taking apart the whole dash and harness?
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    #2
    really? short of tracing the whole thing, put in a 30A fuse and watch for smoke. Pull the fuse if it won't pop and then find what smoked. The danger is this will start a fire. The better way is to trace everything.

    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.

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      #3
      do you have a wiring diagram that you could post photos of? Just the pages concerning this circuit of course: fuse #8, pertaining to radio/clock/dome lights. I'm not sure how (where) to begin tracing even. There's got to be a better way than pulling the whole harness! Best way is to find some nice accessible harness points and check for resistance between there and ground, right? (e.g., 0 resistance between the hot and ground = short).

      ...i was also kinda wishfully thinking that maybe this would be some common issue, and someone would chime in and say, "oh, on every box this happens inevitably! THIS wire tends to rub HERE... pull this piece of trim and take a look!"
      Last edited by BerniniCaCO3; 04-05-2014, 11:45 PM.

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        #4
        I wonder if your car has the same radio low voltage (<12 volts) floating ground as my 85 Town Car with premium sound. Unplug all but one component, reinstall fuse. Keep changing components until the fuse blows (hopefully).

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          #5
          The floating ground is for the speakers, common ground for each set of speakers IIRC

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            #6
            ah i should have mentioned: DID unplug radio at harness. It's the ONLY thing i've ruled out-- but it's not an internal short in the radio

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              #7
              I'm not a fan of the smoke method. It tends to do a lot of damage. Use a lamp in place of the fuse. Disconnect things until the lamp dims or goes out. The lamp will act as a current limiter to keep from melting the wiring. It needs to be something of reasonable current draw, a brake light will do the job fine.

              Pull the visors down and look at the wiring there if yours has the lighted mirrors. It moves a lot and its not uncommon to chafe through.
              86 Lincoln Town Car (Galactica).
              5.0 HO, CompCams XE258,Scorpion 1.72 roller rockers, 3.55 K code rear, tow package, BHPerformance ported E7 heads, Tmoss Explorer intake, 65mm throttle body, Hedman 1 5/8" headers, 2.5" dual exhaust, ASP underdrive pulley

              91 Lincoln Mark VII LSC grandpa spec white and cranberry

              1984 Lincoln Continental TurboDiesel - rolls coal

              Originally posted by phayzer5
              I drive a Lincoln. I can't be bothered to shift like the peasants and rabble rousers

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                #8
                I 2nd or 3rd the tracing method. It took me about 3 months to trace (only working part time and weekends because I have a full time job, oh yeah only if it wasn't raining cause the car was outside!) the short in my cruise control box. I had to unwrap every wire associated to the fuse blowing out. It took time, but I was able to find it. I also have another vehicle to drive to work so I wasn't in a bind and had to fix it right away.


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                I'd rather be a failure at something I love than a success at something I hate.
                George Burns

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                  #9
                  no, I don't have a diagram of a 1990, unfortunately. +1 Gadget's method.

                  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.

                  Comment

                    #10
                    Look at the stuff that's been modified first. Like the wiring behind the aftermarket radio. The stuff that's been pulled out of the original Ford harnesses is the stuff that's the most likely to get fucked.

                    Are your wires that hook up to the radio getting squashed or is a connection grounding out on the radio chassis?
                    Originally posted by gadget73
                    There is nothing more permanent than a temporary fix.
                    91 Mercury CP, Lopo 302, AOD, 3.08LSD. 3g upgrade, Moog wagon coils up front, cc819s in the back. KYB GR-2 police shocks. Energy suspension control arm bushings. Smog deleted.
                    93 F-150 XLT, 302, ZF 5-spd from 1-ton, 4wd.
                    Daily--07 Civic Coupe. Bone stock with 25k miles
                    Wife--14 Subaru Outback. 6-speed.
                    95 Subaru Legacy Wagon--red--STOLEN 1/6/13

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                      #11
                      anyone have a 1990 wiring diagram, or should I just order another off of ebay?

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                        #12
                        Ok looking on this website it says green/yellow is 12 volt constant to the radio hope that helps

                        1990 Mercury Grand Marquis Audio Wire Diagram
                        http://www.modifiedlife.com/1990-mercury-grand-marquis-car-audio-wire-diagram/
                        Question: Where can I find a 1990 Mercury Grand Marquis stereo wiring diagram? What are the 1990 Mercury Grand Marquis radio wiring harness colors? If you're looking to change the radio in your 1990 Mercury Grand Marquis or troubleshoot why your car radio stopped working, we're here to help! Our comprehensive 1990 Mercury Grand Marquis

                        Or maybe this?

                        1990 Grand Marquis No Turn Signals and A/C is warm - GrandMarq.NET - Panther Headquarters
                        http://www.grandmarq.net/vb/showthread.php?t=44707
                        Everything to do with interior and body electrical including headlights and tail lights. CFI specific discussions and AC/heating systems.


                        This might help too

                        Radio Problems - GrandMarq.NET - Panther Headquarters
                        http://www.grandmarq.net/vb/showthread.php?t=43645
                        Everything to do with interior and body electrical including headlights and tail lights. CFI specific discussions and AC/heating systems.


                        Or maybe this?

                        1990 Grand Marquis No Turn Signals and A/C is warm - GrandMarq.NET - Panther Headquarters
                        http://www.grandmarq.net/vb/showthread.php?t=44707
                        Everything to do with interior and body electrical including headlights and tail lights. CFI specific discussions and AC/heating systems.


                        Sent from my '85 Lincolin Town Car
                        Last edited by kodiak; 04-13-2014, 04:41 PM.
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