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One tiny wire providing ALL power to FJ40? Weird that.

Discussion in '40- & 55-Series Tech' started by loosechange, Jul 17, 2017.

  1. loosechange

    loosechange

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    I have a 1972, manufacturing date was June 72. This vehicle has the 350 conversion and I am running a 150 amp alternator straight to the battery the battery goes straight to the solenoid on the starter and I've got a fuse box with all my switches off the battery using fuses and relays a breaker etc.… This is my auxiliary fuse block and switches.

    So the concern I have is I've noticed that there's really nothing that batteries connecting to that's giving the actual vehicle electrical I mean I'm looking at this thing and with one little tiny wire that was hanging down, then I installed it yet it's probably a 12 gauge wire and once I put it to positive everything on this vehicle will work :headlights brake lights, ignition, you name it Everything seems to work now

    let's say everything is running everything is doing great and I pulled 12 ga wire off power (hot)...everything dies ----

    no horn. Wipers doesn't work ...lights doesn't work ignition doesn't work nothing. Literallly one tiny wire powers the entire vehicle doesn't make sense.

    Why does this seem odd?
     
  2. lcwizard

    lcwizard Supporting Vendor

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    it doesn't. The 72 had a 30amp alternator, no need for anymore wiring than that 12 gauge. For older trucks that i need winching or other
    hi amp applications , I run a large capacity relay, contactor or solenoid. I don't advise running 150 amps through a stock harness. Even the
    60 series wasn't designed for that. Relays are your friend unless you prefer fire and smoke
     
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  3. lcwizard

    lcwizard Supporting Vendor

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    You have to realize the Cruisers use an ammeter rather than a voltmeter. The ammeter is wired to show true draw on the entire system.
    One wire feeds the system through the ammeter. Bypassing the ammeter through relays and secondary fuse panels renders the ammeter
    less useful. The ammeter only goes to 30 so trying to run 150 amps through it might prove entertaining in a 4th of July kinda way.
    Ammeters are probably not realistic on modern vehicles, for that reason, which is why the voltmeter took it's place on the 60 series.
    I've seen the wire to the ammeter fry. I'd hate to see the same setup with a 150 amp service.
     
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  4. sggoat

    sggoat

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    Ammeters tell you way more about your electrical system than voltmeters ever will--voltmeters only tell you potential--ammeters will tell you this in addition to what current flow is-they tell you if your turn sigs are flashing, if you brake lights are working, if your b/u light is working,if your parking/headlights are on, and if the alternator is really charging--
     
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  5. loosechange

    loosechange

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    Well I do have to agree that it appears that wiring is still through the ammeter gauge on my dash however I know when I run the vehicle with my hundred amp alternator where it does not register any type of positive or anything it registers negative so it's like it's not even there it's not even registering that I'm getting powered anything so that means the truck is going to Sit more till I see what I need to to do

    I appreciate the replies.
     
  6. loosechange

    loosechange

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    So since I'm here let me ask…

    How do I by-pass the ammeter?
     
  7. Pin_Head

    Pin_Head

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    Since you wired the alternator directly to the battery, the amp meter will no longer indicate charging (deflection to the + side). It will only indicate draw. There is no reason to bypass it, but if you insist, just connect a large gauge wire between the two terminals of the gauge.
     
  8. Coolerman

    Coolerman SILVER Star

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    It'a actually even easier than that to bypass the Amp Meter. Just take the 10ga White wire off it's terminal on the back of the gauge cluster and place it on top of the 10ga White/Blue wire and use the nut you removed to secure it.

    Now back to your wiring mess....

    You should have a fusible link installed on that 1972. Find the 10ga White wire coming out of the main harness near the battery. It should have a weird looking MALE connector. Plugged into that will be a short 14ga 4" Fusible link wire, and plugged into the fusible link, will be a 10ga wire going to the battery + post. The fusible link to there to protect the main charge wires (the white and white/blue 10 ga wires) from a dead short. If your truck does not have the fusible link installed (IE the white wire is hooked straight to the battery + post), you run the risk of a fire.

    A fusible link is sized 4 wires sizes smaller than the wire it is protecting. The main charge wire is 10ga so 4 sizes smaller is 14ga (11, 12, 13, 14) and yes the entire current flow goes through that little 14ga wire. It is short, so the actual resistance is small and does not have much voltage drop, but if you have a dead short to ground the smaller 14ga wire will melt and burn in two before the 10ga wire does.

    I sell the fusible link, the main harness connector and the battery side connector assembly if you need any of that.

    You also should consider protecting the 150 amp alternator charge wire with a fusible link.
     
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  9. lcwizard

    lcwizard Supporting Vendor

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    That's good for a 30 amp system.
    I still don't want an ammeter in my dash that's monitoring 150 amps. I can weld with that. I'm happy enough that a voltmeter is telling me when my alternator isn't charging..or overcharging
     
    Last edited: Jul 19, 2017
  10. lcwizard

    lcwizard Supporting Vendor

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    Since a 150amp alternator would need a minimum 6 gauge, preferably 4, would you still prefer a fusible link over a resetable breaker.
     
  11. Coolerman

    Coolerman SILVER Star

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    Yeah, for wire that size, a breaker or an ANL fuse, is easier to install, and much easier to reset/replace vs. a fusible link.

    When to use a breaker vs a link is a matter of what the circuit is feeding. If the circuit has things like motors (radiator fans) that have high inrush currents, then the link is a better choice to prevent nuisance tripping of a breaker.

    ANL fuses can be had in up to 500 amp sizes and are good for placing in line with the + battery cable, the alternator charge wire, or aux fuse blocks. Resetable Circuit Breakers are available up to 250 amps and I have used them when adding aux fuse block to protect the feed from the battery to the block.
     
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  12. Pin_Head

    Pin_Head

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    Amp meters since the mid to late 70s no longer have high current running through the meter. They use an external shunt that is typically at the battery. People don't tend to notice meters any way. Just give them a big bright idiot light.
     
  13. lcwizard

    lcwizard Supporting Vendor

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    ( except the cruiser of course )
    But they'll need someone with an electronics familiarity to build a shunt for the cruiser ammeter and then the +/- 30 won't really mean much.
    Most of the commercially setup shunts I've found are for older 6v systems moving to 12v. I've seen some ammeters that read 60 =/- amps, and one that reads 100=/-. I haven't seen an ammeter for cars that shows a +/- 150 or 200 yet. There are commercial vehicle gauges for ambulances and firetrucks that do that but again you'll be mounting them in a 2" round hole.
     
  14. Pin_Head

    Pin_Head

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    Cruisers used the fusible link as an external shunt beginning in 1978 with the 50-0-50 meter up until they were discontinued.
     
  15. bikersmurf

    bikersmurf

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    As mentioned, I've got an ammeter in my Ambo that monitors the output of the 215 amp alternator.
     
  16. Coolerman

    Coolerman SILVER Star

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    I often wondered just how much power an Ambulance uses.... Now I know!
     
  17. bikersmurf

    bikersmurf

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    It has a Mitsubishi 215 Amp alternator. I've been told it'll put out 215 Amps continuously and even up to 300 Amps peak when cold. It's a 32 lb beast.
     
  18. 73FJ40

    73FJ40 After another night of rust removal! SILVER Star

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    What kind of belt drives a 215 amp alternator? Do you have to use a roller chain? :rofl:
     
  19. Coolerman

    Coolerman SILVER Star

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    I bet the wiring in that vehicle is a nightmare to troubleshoot! I would love to see a schematic for that vehicle.
     
  20. bikersmurf

    bikersmurf

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    The alternator is driven by an 8 grove serpentine belt that's about 1.25" wide. Wiring of the Cab is Ford. The box wiring is numbered along its length. Closest thing to a schematic is a 3' square 'diagram' behind the door to the electric compartment. It indicates what all the components are and the numbers of any wires going to them.