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  1. #1
    FEP Member Mgino757's Avatar
    Join Date
    Jan 2011
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    Virginia Beach, VA
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    489

    Default 85 GT: Reverse lights blow fuse

    My 85 GT has started blowing #5 fuse with the reverse light connector on the switch, but not when disconnected. With the switch connected, the fuse will blow only when I take it out of reverse. Putting the transmission in reverse will light up the reverse lights, but as soon as I shift out of reverse, the fuse pops. I checked the wiring, it looks fine. I ohmed the two wires on the switch. The ground side has maybe 3 ohms, the white wire side was showing 73 ohms. I tested the switch, it only has continuity when reverse is engaged. Could it be the switch shorting out when shifting out of reverse?
    1985 Mustang GT conv. modified 4180C, Weiand Street Warrior intake, equal length headers, true dual exhaust, 3.55:1 8.8'' rear end, 2003 V6 T5, Ford Racing 10.5" clutch.

    1998 Mustang GT auto. PI swapped. Daily beater

  2. #2
    FEP Senior Member
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    May 2016
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    Lake City Pa 16423
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    510

    Default

    The reverse switch is only an open/close switch. When it is not in reverse, the switch is open. When put in reverse, it closes. The switch provides power to turn on the lights when you select reverse. You said the switch ohms out 3 on the ground side? There is no ground side. It is sending battery power straight to ground and blowing the fuse. There should be no reading from the switch to ground on either side of the switch. You should only see a couple of ohms through the switch when it is in reverse, and nothing when it is out of gear.

    You have a switch shorting to ground when it is not in gear. It will need to be replaced.

  3. #3
    FEP Member Mgino757's Avatar
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    Jan 2011
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    Virginia Beach, VA
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    489

    Default

    I replaced the backup light switch. Problem is fixed.
    1985 Mustang GT conv. modified 4180C, Weiand Street Warrior intake, equal length headers, true dual exhaust, 3.55:1 8.8'' rear end, 2003 V6 T5, Ford Racing 10.5" clutch.

    1998 Mustang GT auto. PI swapped. Daily beater

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