No Electrical Power After Putting The Motor Back In My Car

Discussion in 'Fox 5.0 Mustang Tech' started by bbredstang, Aug 10, 2013.

  1. bbredstang

    bbredstang Member

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    I have a 90GT.

    I had the motor/transmission out of the car to put a new oil pump in. While I had the motor out, I painted the block.

    I just got everything back in and hooked up and there is no power to the car. When I hooked up the battery, there was not the usual mini-spark that takes place hooking up the battery, which I thought was weird prior to jumping in the car to no dome light/power.

    I checked the battery and it tests out fine. I am thinking this is potentially bad grounds. The firewall ground is hooked up to the intake as usual. Perhaps the paint is causing issues with the main ground.

    Any thoughts? Do you think I am going in the right direction, or can anyone else think of other things that would cause this. I was super excited to fire it up........right until the electrical gremlins showed their face!

    Thank you for any tips you may have.
     
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  2. mikestang63

    mikestang63 Mustang Master

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    Get a wiring schematic for your engine, main harness and battery circuit-on this site-

    http://www.veryuseful.com/mustang/tech/engine/

    Check every ground wire starting with the battery, computer and other primary grounds. Then check all of your harnesses. You forgot to hook something up.

    You can start from the battery and work your way back with a DVM on the neg and pos side.
     
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  3. jrichker

    jrichker StangNet's favorite TOOL
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    Did you remove any wires from the starter solenoid?
    Did you reconnect the battery ground to the engine block near the oil filter?
    Did you reconnect the battery pigtail ground to the fender near the windshield washer filler neck?
    Did you reconnect the engine to body ground on the intake manifold to firewall?

    Starter solenoid wiring 86-91 model cars.
    [​IMG]


    [​IMG]

    Fuse links come with a current rating just like fuses. A clue as to what current they are designed for is to look at the size wire they protect.

    Choose the fuse according to the wire size.

    Grounds

    Revised 28-Oct-2012 to add signal ground description & possible problems if it is bad

    Grounds are important to any electrical system, and especially to computer controlled engines. In an automobile, the ground is the return path for power to get back to the alternator and battery.

    1.) The main power ground is from engine block to battery: it is the power ground for the starter & alternator.


    2.) The secondary power ground is between the back of the intake manifold and the driver's side firewall. It is often missing or loose. It supplies ground for the alternator, A/C compressor clutch and other electrical accessories such as the gauges.

    Any car that has a 3G or high output current alternator needs a 4 gauge ground wire running from the block to the chassis ground where the battery pigtail ground connects. The 3G has a 130 amp capacity, so you wire the power side with 4 gauge wire. It stands to reason that the ground side handles just as much current, so it needs to be 4 gauge too.

    The picture shows the common ground point for the battery , computer, & extra 3G alternator ground wire as described above in paragraph 2. A screwdriver points to the bolt that is the common ground point.

    The battery common ground is a 10 gauge pigtail with the computer ground attached to it.
    Picture courtesy timewarped1972
    [​IMG]

    Correct negative battery ground cable.
    [​IMG]

    3.) The computer's main power ground (the one that comes from the battery ground wire) uses pins 40 & 60 for all the things it controls internally: it comes off the ground pigtail on the battery ground wire. Due to its proximity to the battery, it may become corroded by acid fumes from the battery.
    In 86-90 model cars, it is a black cylinder about 2 1/2" long by 1" diameter with a black/lt green wire.
    In 91-95 model cars it is a black cylinder about 2 1/2" long by 1" diameter with a black/white wire.
    You'll find it up next to the starter solenoid where the wire goes into the wiring harness.
     
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    Last edited: Aug 10, 2013
  4. bbredstang

    bbredstang Member

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    Did you remove any wires from the starter solenoid?
    -nothing was removed from the solenoid
    Did you reconnect the battery ground to the engine block near the oil filter?
    -yes, however I am going to remove this ground and sand the block tomorrow to ensure the paint is not conflicting
    Did you reconnect the battery pigtail ground to the fender near the windshield washer filler neck?
    -this wasn't removed, however I am planning to double check tomorrow
    Did you reconnect the engine to body ground on the intake manifold to firewall?
    -yes

    Thanks for the info guys. I am going to work my way through connection by connection tomorrow with a volt meter to see if I can pinpoint the issue. Keep me posted if you think of anything further.
     
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  5. bbredstang

    bbredstang Member

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    So, this morning I learned that I cannot trust the light indicators on my battery tender. I brought my volt meter over and the battery was only reading 1.8V, even though the tender said it was fully charged and ok.

    Grabbed a new battery, tossed it in, and it fired up.
     
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  6. mikestang63

    mikestang63 Mustang Master

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    That's some funny stuff right there. :doh:
     
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