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    #1

    Amp light is always on

    Ever since I bought this car the amp light has been on. The battery was tested and it's good and is only a year old. The alternator (2g) also tested good and apears to be new.

    I started digging into the wiring for it today and found that the white/black thin wire on the plug with the orange/black charge wires was cut inside the harness and covered with electrical tape and loomed over. I reconnected it but that didn't change anything.

    So according to this post, http://www.grandmarq.net/vb/showpost...9&postcount=14 the green/red wire is supposed to be the wire that runs the amp light. It seems to be in good shape and runs into the main harness that atatches to the fuse box under the hood. After that I'm not sure where it goes. Does it ground out somewhere? If it does is it under the hood or the dash?

    Thanks.
    1990 Lincoln Town Car 5.0 H.O.
    Tags: None
    #2
    The circuit runs from the ignition switch, through the AMP bulb, to the red/green wire under the hood. The alternator actually provides the ground to make the bulb go. See if the amp light is on with the regulator unplugged. If it is, there is a short to ground in the wiring somewhere. If its not on, then the issue is something involving the alternator or it's wiring.

    Check the fuse links for the alternator too. Easy way is to take a voltmeter or test light from ground to each of the black/orange wires and to the yellow wire on the regulator plug. Each wire should show battery voltage. You can do this with the alternator unplugged. Car shouldn't be running for this.
    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

    Comment

      #3
      I drove the 91 around for about 8 months with the battery light on... my volt meter showed it was still charging so I kept driving.
      Only after those many months did I notice the charging voltage start to drop lower and lower, so then I replaced the alternator - no more light.
      Weird stuff happens...
      Pete ::::>>> resident LED addict and CFI defector LED bulb replacements
      'LTD HPP' 85 Vic (my rusty baby) '06 Honda Reflex 250cc 'Baileys' 91 Vic (faded cream puff) ClifFord 'ODB' 88 P72 (SOLD) '77 LTDII (RIP)
      sigpic
      85HPP's most noteworthy mods: CFI to SEFI conversion w/HO upperstuff headers & flowmasters P71 airbox Towncar seats LED dash light-show center console w/5 gauge package LED 3rd brake light 3G alternator mini starter washer/coolant bottle upgrade Towncar power trunk pull underhood fuse/relay box 16" HPP wheels - police swaybars w/poly rubbers - budget Alpine driven 10 speaker stereo

      Comment

        #4
        The first 3g on my car did that, it charged but the idiot light was on. Exchanged the alternator under warranty, no more light. Don't know what the problem actually was but it was in the alternator.
        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

        Comment

          #5
          i went thru 4 reman 2g's in 6 years before i did the 3ag conversion

          1986 lincoln towncar signature series. 5.0 HO with thumper performance ported e7 heads, 1.7 roller rockers, warm air intake, 65mm throttle body, 1/2" intake spacer, ported intakes, 3.73 rear with trac lock, 98-02 front brake conversion, 92-97 rear disc conversion, 1" rear swaybar, 1 3/16" front swaybar, 16" wheels and tires, loud ass stereo system, badass cb, best time to date 15.94 at 87 mph. lots of mods in the works 221.8 rwhp 278 rwt
          2006 Lincoln Town Car Signature. Stock for now
          1989 Ford F-250 4x4 much much more to come, sefi converted so far.
          1986 Toyota pickup with LSC wheels and 225/60/16 tires.
          2008 Hyundai Elantra future Revcon toad
          1987 TriBurner and 1986 Alaska stokers keeping me warm. (and some pesky oil heat)

          please be patient, rebuilding an empire!

          Comment

            #6
            Glad that old post is still proving useful.

            I just realized, I know the switched +12 is needed to energize the field coils (not knowing this once caused me a whole lot of trouble a few years back), but I have no idea why the alternator light isn't lit under normal operation! Obviously, the normal current draw through it is very small, but why?
            2012 Mazda5 Touring | Finally working on the LTD again!

            Comment

              #7
              The bulb is bypassed with a resistor to keep it from lighting up normally. When things aren't working, the VR pulls enough current through the bulb to make it light up. Never dissected a regulator though so I'm not sure exactly how it functions internally to explain why this is.
              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

              Comment

                #8
                Huh, put that way it sounds like the resistor must have lower working resistance than the bulb... seems odd in a way, since those diagrams seem to have it labelled "510 Ohms". I suppose I could always just measure one to find out!
                2012 Mazda5 Touring | Finally working on the LTD again!

                Comment

                  #9
                  bulb resistance changes with heat, so that may not give you what you're after. Also, just having a resistor across the bulb doesn't mean current bypasses the bulb totally, it only needs to have a low enough current draw to not cause the filament to glow. In paralell, the resistance is always lower than the lowest single element in the chain. Formula is R1 + R2 / R1 * R2
                  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

                  Comment

                    #10
                    Originally posted by gadget73 View Post
                    The circuit runs from the ignition switch, through the AMP bulb, to the red/green wire under the hood. The alternator actually provides the ground to make the bulb go. See if the amp light is on with the regulator unplugged. If it is, there is a short to ground in the wiring somewhere. If its not on, then the issue is something involving the alternator or it's wiring.

                    Check the fuse links for the alternator too. Easy way is to take a voltmeter or test light from ground to each of the black/orange wires and to the yellow wire on the regulator plug. Each wire should show battery voltage. You can do this with the alternator unplugged. Car shouldn't be running for this.
                    I unplugged the regulator and the light is still on. So tomorrow, while i'm swapping intakes, injectors, and the comp, I'll test the links for the alt.
                    1990 Lincoln Town Car 5.0 H.O.

                    Comment

                      #11
                      well if you unplugged the regulator (small plug) and the light is still on, you have a wiring fault somewhere else. With the regulator unplugged, there should be no current flowing through that bulb.
                      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

                      Comment

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