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Thread: 175 amp Mega Fuse and Dashboard Light

  1. #1

    Default 175 amp Mega Fuse and Dashboard Light

    '95 Mystique V6 5 speed. 300,319 miles. In great shape, garaged from new until 2007... only to make room for my 2004 Cadillac CTS, V6, 5 speed.

    Alternator was whining for last 3 years, since 240,000 miles. Battery was always being charged, and no warning lights, so I kept driving with the whine.
    Last week, battery dashboard light illuminated. I figured alternator finally went. Drove home and parked car.
    Took out alternator. (What a ). Had it tested. NG. Bought new remanufactured, and installed.
    Started car. Battery dashboard light was not illuminated, so I was initially happy, but the battery was not charging. 11.8 volts across battery when engine running. 12.2 volts engine off. The battery dashboard light did not illuminate either with key in ON/accessory position, or with the car running !!!
    Found 175 amp Mega fuse blown. Replaced it. Checked for continuity between cable at the alternator before the megafuse, and the positive battery cable after the megafuse. I had continuity. Good, I thought.
    Connected battery.
    Turned key to ON/accessory position. No illumination of battery dashboard light.....
    Started car. No illumination of dashboard light..... Still no charging of the battery. 11.8 volts with car running. 12.2 volts engine off.
    Disconnected the battery and the cable from alternator. No more continuity between alternator cable and battery cable.
    Help !
    I want to keep this car.
    Does anybody have any ideas?
    Cables look good, no worn insulation, but I still need to trace the positive battery cable and inspect it throughout its entire length. Negative cable looks good, and looks good to ground.
    Battery is only 2 years old, and is holding a 12.2 volt charge, cables disconnected.
    Any ideas, please.
    I'd hate for my next step to be posting pictures in an attempt to part-out the car.....

  2. #2
    Join Date
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    Twin Cities, MN
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    Did you check the Megafuse the second time? If that is blowing there has to be a reason for it. I once had my EGR tube melt through the casing of the positive battery cable and short it out.
    2009 Honda...

  3. #3

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    Yes, the megafuse is blown again.
    I am kinda looking to see if someone knows of a common area where I could be blowing this 175 amp fuse.
    Or if I am totally overlooking something else.
    I also took the new remanufactured alternator back to shop where I bought it, and it tested good.
    In reviewing this site and reading all the good help, I haven't come across a reason why the battery dashboard light is not illuminating anymore.
    I was driving to work one morning when light came on. Turned around, drove home and parked car.
    After I removed alternator and installed new one, dashboard light does not even illuminate with the key in the ON/accessory position.

  4. #4

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    Quote Originally Posted by RTRT View Post
    Yes, the megafuse is blown again.
    I am kinda looking to see if someone knows of a common area where I could be blowing this 175 amp fuse.
    Or if I am totally overlooking something else.
    I also took the new remanufactured alternator back to shop where I bought it, and it tested good.
    In reviewing this site and reading all the good help, I haven't come across a reason why the battery dashboard light is not illuminating anymore.
    I was driving to work one morning when light came on. Turned around, drove home and parked car.
    After I removed alternator and installed new one, dashboard light does not even illuminate with the key in the ON/accessory position.
    Try checking for a short like this:
    http://www.youtube.com/watch?v=pjXt7...eature=related
    CHECK FOR SHORTS
    Using a probe light
    Disconnect Neg. cable on battery.
    Attach alligator clip from probe or test light to the neg. cable
    Stab the tip of the probe in the neg. battery terminal
    If light is on , there is a short
    Remove fuses until light goes off.

    Another thing , remove the battery and the battery holder. Then check all of the red wires that go to the fuse box(engine bay fuse box) ..Strip the plastic insulation..I had some touching because battery acid dripped on them and melted the insulation. Mine is a 4 cylinder but the battery setup + fuse box should be similar.
    97' ZETEC Contour, 2.0L, 16V , DOHC ,VIN 3,MTX75 ,5 speed
    Mods: JE 10.5:1 Pistons,Eagle Rods,Custom SVT Longtube headers,Spec Stage 2 clutch, Air intake,Mangaflow full exhaust,ThunderVolt 8.2 ,Accel coil,Aeromotive FPR,24# inj ,VMP tune with X3.

  5. #5

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    Quote Originally Posted by Redlineracer12 View Post
    Did you check the Megafuse the second time? If that is blowing there has to be a reason for it. I once had my EGR tube melt through the casing of the positive battery cable and short it out.
    WOW , I shouldn't of read this!!! While I was putting my air intake back on I touched the pos. cable and sure enough..SPARKS! The damn egr tube melted through the positive battery cable . What a paint in the butt to remove that! So RTRT make sure you check that!

    P.S This would explain why my car died on the freeway
    97' ZETEC Contour, 2.0L, 16V , DOHC ,VIN 3,MTX75 ,5 speed
    Mods: JE 10.5:1 Pistons,Eagle Rods,Custom SVT Longtube headers,Spec Stage 2 clutch, Air intake,Mangaflow full exhaust,ThunderVolt 8.2 ,Accel coil,Aeromotive FPR,24# inj ,VMP tune with X3.

  6. #6

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    My sister's 95 Mystique Duratec 5 speed has 12.5 volts running, which is too low. I guess I will first check the megafuse and the egr tube melt (car had new master cylinder installed recently, maybe something moved too far.) Her battery light comes on in Run position but not when running...
    1998 Mystique LS 2.5 Duratec ATX
    1985 Dodge Lancer ES Turbo 2.2
    1991 Taurus SHO, 45kmiles

  7. #7
    Join Date
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    Location
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    the mega fuse has nothing to do with the function of the dash light other then if it blows its going to cause the light to turn on.

    now if the 3 wire connector isn't plugged in or not seated correctly causing it to not connect then the dash light will not work at all. also if there is an issue with the cluster and its not working then the dash light will of course not work and the alternator will not charge. have you checked the bulb? you need to get a service manual and follow the pin point tests.

    also just a note, not sure on the V6, but on my 95 Mystique with the I4 there was a second wire on the B+ terminal other then the main battery cable. perhaps its the same on the 95 V6 and it was missed?

    also the single wire on the alternator can cause issues, iirc. either way you need to run some pin-point tests to identify the issue.
    - 12 Focus SE
    - 95 Mystique LS <-sold
    - 99 Contour SE Sport <- traded in 2/13
    - 99 Contour SeVT <- 3L/NPG Turbo
    - 2k Contour SVT - #2137

  8. #8
    Join Date
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    Quote Originally Posted by acontour View Post
    WOW , I shouldn't of read this!!! While I was putting my air intake back on I touched the pos. cable and sure enough..SPARKS! The damn egr tube melted through the positive battery cable . What a paint in the butt to remove that! So RTRT make sure you check that!

    P.S This would explain why my car died on the freeway
    I didn't even think that the zetec wiring came as close to the egr valve/tube as it does on the duratec? but bottom line manu miss run the battery cable on the duratec and it contacts the egr valve.
    - 12 Focus SE
    - 95 Mystique LS <-sold
    - 99 Contour SE Sport <- traded in 2/13
    - 99 Contour SeVT <- 3L/NPG Turbo
    - 2k Contour SVT - #2137

  9. #9

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    Quote Originally Posted by BrApple View Post
    I didn't even think that the zetec wiring came as close to the egr valve/tube as it does on the duratec? but bottom line manu miss run the battery cable on the duratec and it contacts the egr valve.
    The Zetec wiring comes prettly close to the egr tube(where it connects to the valve) but not as close as mine did. When I re-installed everything after the rebuild I messed up and got it way to close to the tube. Learned my lesson.
    97' ZETEC Contour, 2.0L, 16V , DOHC ,VIN 3,MTX75 ,5 speed
    Mods: JE 10.5:1 Pistons,Eagle Rods,Custom SVT Longtube headers,Spec Stage 2 clutch, Air intake,Mangaflow full exhaust,ThunderVolt 8.2 ,Accel coil,Aeromotive FPR,24# inj ,VMP tune with X3.

  10. #10

    Default Solution

    Hi Guys,

    Just thought I would tell you what I did to solve problem. My Mystique has been running and charging the battery properly now for the last month and 2400 miles.

    The wiring from the alternator to the battery on my 95 V6 was originally as follows:
    Alternator to MegaFuse to Starter to Positive Battery Cable

    I ran a new 48 inch battery cable from
    Alternator to MegaFuse to Positive Battery Cable connection.
    I mounted the new MegaFuse directly at the battery with insulation.

    The starter is still getting power from one cable from the original battery cable connection.

    Car is charging with 14.0 volts with engine running.
    No more blowing of the MegaFuse.
    The dashboard light is on, but I figure this is because the original circuit has been bypassed.
    No issues under full load: defrosters, windshield wipers, headlights, directionals, radio all on.
    All is good and I am continuing my 106 mile daily roundtrip commute with 302,700 miles now.

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