Help! Car completely died on the road. No power

Discussion in 'Mustang Chit Chat' started by theRedStorm, Apr 9, 2021.

  1. DieHarder

    DieHarder Member

    Some thoughts below regarding troubleshooting. Somewhat concerned that you're drawing 4 amps (assuming key off). That's high IMHO and will discharge any battery in nothing flat.

    1) Reverse what you've done (put the wiring back to stock) and recheck/report symptoms. Any change?
    2) Troubleshoot the power circuits (See Step 5 below for references). Appears you already have a volt/ohm meter... Follow the Pin Point Tests - record results; if needed disconnect lines; check resistance/connectivity of the wiring. (For instance there is a fuseable link in the blue jacketed battery cable (that can also get corrosion in it)). You should see less than an Ohm from one end to the other on any wiring you check. Reconnect. Any change?
    3) Recheck the SJB and the connectors that plug into it. Obviously, there is corrosion which tends to increase resistance or if completely bad can create an open condition (no voltage/signal). You can try using dielectric grease to improve connectivity of the connections to troubleshoot but it's not a long-term solution.
    4) If symptoms change at any step record what it was (voltage, resistance, open/short) and report.
    5) If nothing changes I would go back to basics. Make sure the battery is working first. Then determine where power is or is not and why. Sections 414 (Battery -; 303-06 (Starter -; Wiring diagrams ( System.pdf&p=2) & 419-10 (SBJ Principals/Operations - ) address the majority of what you're working on to troubleshoot this problem. I would think you should be able to narrow it down to bad wiring or a module. Either can be replaced (or terminals cleaned and put back in service; depends on how bad it is). If you can find a good SJB at a decent price probably worth swapping it but I would verify symptoms to ensure you're not just throwing money away for another issue like shorts or bad grounds.
    6) If all else fails may be worth an hour of troubleshooting at the dealer provided they have someone who can actually troubleshoot electrical systems. Some understand what they're doing; others not so much. That would at least help you narrow it down to a couple of likely suspects.

    Hope this helps....
    theRedStorm likes this.
  2. theRedStorm

    theRedStorm forum member

    Solved my problem fellas. The wire connecting to the Fusebox (main power connector) was damaged from the bottom of the cover. I cleaned up the wires and fixed the connection. It was basically hanging together and whenever bumps happen, it'd disconnect. Whenever I'd shake the wires by removing the ground, itd temporarily reconnect em. ‍♂️
    Such a simple fix HOLY COW

    She up and running like a CHAMP again
    Bullitt2954, nyuk98GT, golkhl and 3 others like this.
  3. theRedStorm

    theRedStorm forum member

    Thank you all for the help!!!!!! :chewie:
  4. DiMora

    DiMora More Is Better

    I've got a similar issue now...will report back if I can find the fix. Ugh.
  5. Pentalab

    Pentalab forum member

    4 ga wire is not rated for 135 amps...well it might, barely, if 105 deg C insulation is used. It really should be bigger ga wire, to minimize Vdrops.
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