Neg. Cable Route With 5.0

Discussion in 'Fox 5.0 Mustang Tech' started by bigjimmy, Jun 19, 2013.


  1. bigjimmy

    bigjimmy Member

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    I just threw away a home-brewed cable that had failed--it was about 42" long and went more or less straight to the block, with a secondary neg. cable going to a ground next to the batt. on the fender. This was amateur-ish, so I tossed it, and bought a cable from NAPA, but it is 60" long and will need a secondary wire lengthened to fit.
    Was there some specific route for the neg. cable or should I just wing it?
  2. JasinC19

    JasinC19 What hole is this!?!

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  3. jrichker

    jrichker StangNet's favorite TOOL SN Certified Technician Founding Member

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    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. The clue to a bad ground here is that the temp gauge goes up as you add electrical load such as heater, lights and A/C.

    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]
  4. Grabbin' Asphalt

    Grabbin' Asphalt Mustang Master

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    Is that meaning a slight change, major change or ANY movement at all??
  5. jrichker

    jrichker StangNet's favorite TOOL SN Certified Technician Founding Member

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    Usually it's a significant change. Use the voltage drop tests as described below if you have any doubts.

    See http://assets.fluke.com/appnotes/automotive/beatbook.pdf for help for help troubleshooting voltage drops across connections and components. Be sure to have the maximum load on a circuit when testing voltage drops across connections. As current across a defective or weak connection, increases so does the voltage drop. A circuit or connection may check out good with no load or minimal load, but show up bad under maximum load conditions. .

    Voltage drops should not exceed the following:
    200 mV Wire or cable
    300 mV Switch
    100 mV Ground
    0 mV to <50 mV Sensor Connections
    0.0V bolt together connections

    [​IMG]
  6. bigjimmy

    bigjimmy Member

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    Thanks for the responses, I finally used a slightly shorter main cable that I got from NAPA--the pigtail to the fender was lengthened, and now it fits and looks like a factory part--they car is acting perfectly. Thanks for the help--I am kinda knowlegable but it helps to get your input.

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