Battery Relocation Wiring Question

Discussion in '2005+ Mustang GT 4.6L Tech' started by 1950StangJump$, Jan 25, 2020.

  1. 1950StangJump$

    1950StangJump$ forum member

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    I see a few good threads for relocating the battery to the rear in an S197. But, some seem harder than they need to be, so wondering what I am missing?

    Right now, with the battery up front, it has the main positive cable (2AWG?) coming from the battery, as well as the one main ground cable (4 AWG?). Also, I have previously run a dedicated 1/0 gauge positive from the positive battery terminal to my 215 amp PA Performance alternator - fused to 250 amps.

    To relocate, I was going to:

    1. Simply run one 1/0 gauge wire (fused to 300 amps) from the battery in the back to a distribution block up front. That block will feed both the original OEM 2 AWG positive wire and the dedicated alternator 1/0 AWG wire I had previously installed.
    2. Ground the battery to the body in the back (spare tire well?) with a 1/0 AWG wire.
    3. Ground the original OEM 4 AWG ground wire up front (that had gone to the battery) to the strut tower.
    I see lots about running dedicated alternator power to the rear, dedicated starter power to the rear, and/or grounds from the battery in the back all the way to the engine block up front. I also see folks running solenoids/relays for the power wires. Is that necessary for a street car? BTW, not tracking the car, so the cutoff switch is definitely out.
     
  2. 07 Boss

    07 Boss Senior Member

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    It is my understanding that people run the alt wire all the way back because they are running a cut off switch. If the alt wire goes right to the distribution block there is no way to cut the power from the alt to the motor. So if you cut the battery from the system it will continue to run off the alternator. Running the alt wire to the back and then one up to the distribution block allows you to place the cut off between the motor and both the alternator and the battery.
     
    HOLLYWD69 and Scott like this.
  3. 07 Boss

    07 Boss Senior Member

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    It is my understanding that people run the alt wire all the way back because they are running a cut off switch. If the alt wire goes right to the distribution block there is no way to cut the power from the alt to the motor. So if you cut the battery from the system it will continue to run off the alternator. Running the alt wire to the back and then one up to the distribution block allows you to place the cut off between the motor and both the alternator and the battery.
     
  4. 1950StangJump$

    1950StangJump$ forum member

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    Yea, that makes sense, especially after I reread the threads where a solenoid and cutoff switch were used.

    My last remaining question would be about the ground .... whether picking one up a few feet from the battery in the trunk is sufficient, or whether the ground wire needs to be run back up to the engine block?
     
  5. GlassTop09

    GlassTop09 Member

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    It will depend on where you attach the ground as it'll need to be able to flow the 300-400 amps that the starter will pull thru it w\o a lot of current drop. I would assume that anywhere on the main unibody structure would be good but I'm assuming here...……….

    If it were me I would run a sufficiently sized battery ground cable back up to where the original battery ground cable is terminated under the hood to ensure the integrity of the battery ground w\ the rest of the electrical system to play it safe...……….
     
    Scott likes this.
  6. 1950StangJump$

    1950StangJump$ forum member

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    300-400 amps for the starter? I was planning to run a 300 amp fuse on the battery, which seems to be common. You sure about that 300-400 figure?
     
  7. datmbn

    datmbn forum member

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    Starter= 1400W
    1400W/12V=117A with good battery
    1400W/10V=140A with extremly bad battery
    With some saftymargings never more then 150A
     
  8. 1950StangJump$

    1950StangJump$ forum member

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    10-4, thank you
     
  9. RED09GT

    RED09GT Senior Member S197 Team Member

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    On my fox body, I had a 1/0 ground at the rear of the car and also ran a 2 gauge wire from the same lug up to the bellhousing after I had troubles starting the car. This improved things quite a bit.
     
  10. 1950StangJump$

    1950StangJump$ forum member

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    Yea, the posts/threads I found where guys ran a ground up to the front were all fox bodies and SN95s. Didn't find anyone who said that was needed for the S197, so not sure.
     
  11. Racer47

    Racer47 Doesn't have much to say S197 Team Member

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    Its usually not needed. But I did it anyway. I ran power up to a distribution block on the firewall. I ran the ground from the battery to the motor mount. I took the original battery ground and ran it to the shock tower. I eliminated the smallest gauge ground wire that originally went to the shock tower.

    End result, main power cable bigger, main ground bigger, ground from motor to shock tower bigger too.

    Chasing electrical issues is a pain. I'd rather spend the extra money and make it as good as possible. Mine has been this way for a few years now with no issues. Moving the battery to the trunk moved 1% of weight to the rear and off the nose.
     
    Scott likes this.
  12. 1950StangJump$

    1950StangJump$ forum member

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    My intent was to do everything you just said .... except was going to run the ground from the battery to a spot on the body in the trunk rather than up to the motor mount.
     
  13. DiMora

    DiMora More Is Better

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    I used a car audio power distribution block on the firewall to hook up the alternator, etc.
     
  14. 1950StangJump$

    1950StangJump$ forum member

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    How did you run your grounds?
     
  15. kerrynzl

    kerrynzl forum member

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    Go down to your local U-Pull and cannibalize the battery cables out of a BMW [E36] They have a trunk mounted battery, and decent cables that are designed for reliability
    I get them for about $30. Including the Ground cables.

    Now the main cable on a BMW goes to a Jumper terminal block on the RF inner fender [approx. the same position as an s-197 battery] so grab this as well.
    All the cables that normally go to the battery can now attach to this. And the main cable goes back to the trunk. AND you have a jumper cable terminal [also for timing lights etc]
    see attachment.
    BMW terminal jumper block.PNG
     
  16. 1950StangJump$

    1950StangJump$ forum member

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    Thanks, but I have a kit already that consists of a 20 ft 1/0 AWG welding cable that will run from the trunk to a distribution block (that I already have) where the battery is now.

    That same kit has a 4 ft 1/0 welding cable for the ground - so that the battery can be grounded to the frame or body in the trunk. The question for me is whether I spend $50 for another 20ft line to run a ground from the trunk/battery to the engine block also.
     
  17. kerrynzl

    kerrynzl forum member

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    The frame/body is one of the best grounding systems ever . What lets it down is all the bad connections in series.
    [battery to frame = 2 connections & engine to frame = 2]

    Most OEM body connections are to a welded nut in the body [a bolt through 2 washers each side of a hole isn't enough]
    Try and find a factory threaded /welded nut in the body and clean the thread and remove a bit of paint for a washer to ground.

    And use star washers not ordinary washers or spring washers [Star washers ground better]
     
    1950StangJump$ likes this.
  18. 1950StangJump$

    1950StangJump$ forum member

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    I have a PA Performance 215 amp alternator. I have fused it to 250 amps, under the idea that a problem there will blow the fuse shortly after the alternator's advertised max output.

    But, do I want to fuse the battery higher than that? I had thought 300 amp fuse. But, I'm second guessing myself . . . do I need to go higher than the alternator as planned, or do I only fuse the battery enough to cover the starter, e.g. 200 amps?

    In the end, is it irrelevant, i.e. would 300 be low enough to blow before any major damage occurred anyway in the event of a problem?
     
  19. datmbn

    datmbn forum member

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    I have can not imagining that a 215A generator delivers more than 200A at normal voltage.
    When you fuse a generator, you want the generator to be able to release the fuse before it burns itself.
    I would have chosen a fuse of 200A.
     
  20. 1950StangJump$

    1950StangJump$ forum member

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    Thought I'd double back to this after lots of research and phone calls to the alternator manufacturer and even several fuse manufacturer phone calls. Bottom line, you want a "slow blow" fuse on the battery.

    Obviously, it has to be big enough able to handle the starter's 120-150 amps while not being so big as to let the line melt. This is where "fuse to the line" comes in.

    But, when you first start to turn the starter over, you actually get a direct "short" to the battery for milliseconds. For those split seconds, you get the full battery cranking amps, in theory. Then, as the motor begins turning, you are still above the 150 amps in some capacity as you overcome inertia of the still motor. That's why, if the fuse was a "quick blow," even 300 amps wouldn't work.

    In theory, all ANS and MEGA fuses are slow blow. But, you just don't know the time delay is with generic fuses. So, I went with the 200 amp MEGA Littelfuse. According to the time delay numbers they publish, it will handle up to 1200 amps for a split second before coming down rapidly to the 1 second mark. For 1-15 seconds, it will still not blow until 200%. After 15 seconds, it blows at about 135%.

    With those numbers, in reality, I could have gone with a 160 amp, as the 135% seems to represent some cushion. But, PA Performance recommends a 200 amp fuse on their 200 amp alternator, so I wanted to keep the two fuses the same.
     
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