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  1. #1

    Default charging question or lack of

    I have an 86 mustang. I did a wire tuck on it and put the battery in the back.
    right now I am working on tuning the engine(megasquirt not fun for the knowledgeable like myself)

    After running the engine for about 20 minutes or and turn it off, then try and turn it back on it will barely crank, like a dead battery.
    I put the charger on it and try again the next day it will fire up and run, then after 20 minutes or so won't crank again.

    I have had the alt tested and it is working, I have a new battery so I am assuming it is something with my wiring that is the culprit.
    Any ideas on where to start?
    All ideas welcome

    Thanks

    Todd

  2. #2
    FEP Super Member erratic50's Avatar
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    Default

    is the battery good or does it have a bad cell? Sometimes they go dead when not on the charger all by themselves due to a draw from a bad cell.

    from there....... fox repair 101 ... throw away the piece of crap factory ground strap and get a new one. They always LOOK fine when frequently they are far from it.

    One alternative is to run a ground from where the main cable attaches to the motor over to the K member somewhere. Also the 4 wire bundle attached to the fender from the factory.... home run that to the negative post of the battery. A second but and a loop works well.

    Once you have those bases covered, make sure your wires going to the alternator are good and the leads aren’t half burned up.

    86 alternators are internally regulated. Is the alternator you’re using correct?

    How much current does your ignition and stereo and wipers and lights, etc, draw?

  3. #3

    Default

    Battery is brand new
    I have a ground strap head to body on both heads
    I have a cable from timing cover to frame and a cable on the other side block to frame, so four grounds there and the one from battery to quad shock bolt sanded and shiny all of them.

    The alternator plugs into the bracket and wiring harness and it tested that it works, other than that I don't know if it is the correct one. I am assuming it is for now since the car ran prior to disassembly

    what do you mean a loop works well.
    I have the battery in the trunk and my battery grounds are going to the horn bolt on the driverside.

  4. #4

    Default

    You got battery in trunk and a 2G alternator? That's a problem; it's barely able to move electrons a couple feet tot the factory battery location. What gauge wires did you use to run battery to trunk? I use 1/0 welding wire minimum. Plus I run both wires all the way back to the bay, (engine), rather than grounding the battery to the frame.

  5. #5

    Default

    I had an 86 convertible 20 years ago. I did basically the same thing(battery in back) and never had an issue,
    but this is different in that after 20 minutes of running turn off then back on it won't crank the starter or barely moves it.

    How much better will battery to block be versus to frame? I have full length sub frames welded in.

  6. #6

    Default

    I'd start with "clamp meter" and verify cranking current.
    I at first thought you have "heat soak" but you didn't mention headers...

    Anyhow, measure cranking amps on first start and another after its hot.

  7. #7
    FEP Super Member erratic50's Avatar
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    Quote Originally Posted by toddf View Post
    Battery is brand new
    I have a ground strap head to body on both heads
    I have a cable from timing cover to frame and a cable on the other side block to frame, so four grounds there and the one from battery to quad shock bolt sanded and shiny all of them.

    The alternator plugs into the bracket and wiring harness and it tested that it works, other than that I don't know if it is the correct one. I am assuming it is for now since the car ran prior to disassembly

    what do you mean a loop works well.
    I have the battery in the trunk and my battery grounds are going to the horn bolt on the driverside.
    good info - had no way to know any of it.

    I was suggesting redoing how the ECU grounds are done to avoid a common issue down the road

  8. #8
    Moderator wraithracing's Avatar
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    First once a vehicle starts, assuming the alternator is putting out enough voltage, the battery is essentially out of the loop in regards to providing power to the vehicle. The alternator should provide all the charge needed and any excess should be able to maintain the battery at full charged voltage of @ 13.2 amps.

    If the battery shows less than @13.2 after shutting off the engine for the 20 minute time frame you mention that shows that the battery is being drained by the electrical system because the alternator is not providing enough "juice" to run all your electrical needs. If the battery shows less than 12.6 volts it is technically discharged at that voltage.

    If the battery is at or around 13.2 volts, then you are not discharging the battery and you most likely need to look at your power wire to the starter/solenoid and your battery/starter grounding.

    What you describe sounds like either a heat soak issue with the starter than can be alleviated with a new/better starter and/or additional heat shielding. You don't state what type of starter, but I am guessing a stock style and not a later model gear reduction starter. I personally like the gear reduction starters, especially with a rear mount battery. I would also recommend removing the ground strap to the timing cover as it does very little in my experience due to the aluminum timing cover not grounding as well as the iron block. Move that ground strap to one of the mounting bolts for the starter and see if that helps. Grounding the starter directly is a good practice no matter where your battery is mounted. Good Luck!
    ​Trey

    "I Don't build it hoping for your approval! I built it because it meets mine!"

    "I've spent most of my money on Mustangs, racing, and women... the rest I just wasted."

    Mustangs Past: Too many to remember!
    Current Mustangs:
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    1982 GT Stalled RestoModification
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    1986 GT Under going Wide Body Conversion Currently

    Current Capris:
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    1982 Capri RS 5.0/4spd T-top Full Restoration Stalled in TX
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  9. #9
    FEP Super Member erratic50's Avatar
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    Default

    I assume Trey means volts

  10. #10
    FEP Super Member gr79's Avatar
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    Views of how one factory routed wires inside car from trunk.
    Was at a pic a part the other day.
    Snapped a few shots of a BMW 325's wiring inside. Battery in trunk.
    Views of wiring at side of rear pass seat, wheel well area down to door sill plastic conduit.
    Yard price is 35.00 for a main harness.
    Going back there this week for a spare 1992 Escort non-cassette AM/FM radio.
    Will take shot of battery connections and battery ground point if possible.Attachment 124070

    Attachment 124071

    Attachment 124069

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