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  1. #1
    New User 1985 Cobra's Avatar
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    Default Battery Ground Cable

    I have a stock 1985 Mustang and having some electrical issues - the temp and oil pressure gauges rise to HIGH when the lights/fog lights are on. I changed the negative cable (used a universal cable) this spring and this is when the issue started. The original one that was on the car was attached to the block on the passenger side. I wanted to change this out with a proper negative cable so I bought one made for the car but it is only 20" and is not long enough. I know that Ford does not make this replacement any longer so wondering if the 20" cable is designed to connect to somewhere other than the block. To reach the block - I will need a roughly 30" cable.

    1. Should the 20" cable to connect to the started or somewhere other than the block
    2. The cable I purchased looks correct since it has the secondary small cable (I think it is to connect to the TSAD
    3. Should I purchase a good longer cable and connect directly to the block.

    Another small issue - the bolt to connect to the block is too large for the connector (have to thread it through with a ratchet) - This is why I am thinking this cable is designed to connect to another ground area.

    Can someone please offer some advice? Thank you!

  2. #2
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    Default

    The gauge problem is likely the IVR. When you increase the load (lights on) the alternator puts out more voltage. The higher voltage is not being properly compensated by the IVR (instrument voltage regulator). It's the part on the back of the gauge cluster with a 9 volt battery type connector. The dash gauges operate on 6 volts (5 bolts in this case).
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  3. #3
    New User 1985 Cobra's Avatar
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    Default

    Quote Originally Posted by KevinK View Post
    The gauge problem is likely the IVR. When you increase the load (lights on) the alternator puts out more voltage. The higher voltage is not being properly compensated by the IVR (instrument voltage regulator). It's the part on the back of the gauge cluster with a 9 volt battery type connector. The dash gauges operate on 6 volts (5 bolts in this case).

    Thanks KevinK,

    Would a faulty IVR also cause the time display and the Shift light to flicker?

    Thanks,

  4. #4
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    Quote Originally Posted by 1985 Cobra View Post
    Thanks KevinK,

    Would a faulty IVR also cause the time display and the Shift light to flicker?

    Thanks,
    Probably not on those.. The shift light is a bulb. I forget what circuit operates that. Maybe the tach. The tach signal comes from the engine but likely something converts it to on/off. That would be done by the dash area so it's possobly it could be IVR related.

    I'm not sure if the clock is LED backlit or just LED text segments. LEDs use a lower voltage than 12 volts so they would have its own power supply someplace.
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    14 Mustang CS/GT, 15 F150 FTX Tuscany, 16 F250 Crewcab, 67 Tbird 47K miles

  5. #5

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    The ignition switch would cause all of these issues as well. Poor connections increase the resistance to a curcuit which will skew guages and explain the flickering.
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  6. #6
    FEP Super Member erratic50's Avatar
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    Default

    Go to a welding supply shop and get 0 gauge welding ground wire and connector. Get a battery terminal from Mcparts store.

    Buy a new engine to firewall ground strap or wire from stock ground attachment point to K member or core support or frame.

    This should eliminate the most common possible ground problems

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