77 fj40 alternator

Discussion in '40- & 55-Series Tech' started by Lukedog, Jun 28, 2010.

  1. Lukedog

    Lukedog

    Messages:
    7
    I have a 77 fj40 and the alternator stopped charging, i replaced with new one and still no luck, i'm thinking may be voltage regulator, or a wire, how can i bypass or test my regulator or troubleshoot my alternator, had it tested and its working on the machine.
  2. Lukedog

    Lukedog

    Messages:
    7
    I really dont understand the wiring on the altenator, is there suppose to be a positive feed going through the plug to the voltage regulator or just negetive ??? :meh:
  3. mightyjoetongue

    mightyjoetongue

    Messages:
    47
    Location:
    Washington
    Do you have a wiring diagram? I am looking at one for a 69 -71, but I am not sure if they are the same wiring configuration. Also do you have a multi-meter?
  4. Lukedog

    Lukedog

    Messages:
    7
    I have a multimeter and found 2 diagrams but are diffrent,
  5. Lukedog

    Lukedog

    Messages:
    7
    the diagram i have says that the black yellow wire on the voltage regulator plug is Positive, but thats not the case.. It ties into ground.
  6. mightyjoetongue

    mightyjoetongue

    Messages:
    47
    Location:
    Washington
    First I wouldn't bypass the regulator, this could cause the alternator to full field(basically max out put) and it could start an electrical fire in you vehicle. Your going to want a legit diagram, if they are aftermarket sometimes the wires are mislabeled, or they could the wrong years, I am not sure. I am also not 100% with original FJ40 regulator setups, the diagram I have for 69-71 has an odd setup, with a wire running through a gauge at the instrument cluster. My vehicle has a V8 conversion w/ a GM alternator. You can eliminate wiring as an issue with a couple different checks. 1. Check available voltages at the regulator and alternator connectors, 2. Unplug the connector at the alternator and the regulator and check continuity between the wires, place one lead in one wire at one component connector, then place the other lead in each wire at the other component to see if there is continuity(when you find a continuous wire right it down and make your own diagram),this will also help identify which wires go where, given your diagrams may be inaccurate. Do this for all the wires and it should give you a good idea. But a proper diagram to compare what you find against would really help. You can also do a voltage drop across the large gauge wire from the alternator to the battery, with the engine running and the meter on VDC, place one lead at the pos. bat. terminal and the other at the connection at the alternator. I think the spec. is .02v per foot of wire. Hope this has helped. Sorry I am not more familiar with the vehicle setup.
  7. Pin_Head

    Pin_Head

    Messages:
    11,634
    Location:
    OC, CA
    There are only 3 wires on the alternator and only 2 are necessary. The large white wire with blue stripe is the power output to the battery +. The white wire with green stripe is the field wire from the voltage regulator. The white wire with black stripe is a ground wire, but this is redundant and not necessary if the ground path from the engine block to the frame is OK. The ground is the negative connection to complete the circuit.

    For testing the alternator, you can temporarily jump between the B+ lug on the alternator and the F lug (field). The voltage output should jump up to over 14 V if the alternator is putting out power. Dont run it like this for long unless you need to charge up the battery, then only run it unregulated for 15 minutes.
  8. Lukedog

    Lukedog

    Messages:
    7
    The white green wire, is it suppose to have a positive current from the voltage regulator or negative?
  9. Pin_Head

    Pin_Head

    Messages:
    11,634
    Location:
    OC, CA
    It really wouldn't matter, but the only way it comes is it has a positive voltage potential with respect to ground, just like everything else on the cruiser.
  10. Coolerman

    Coolerman SILVER Star

    Messages:
    4,827
    Location:
    Paint Lick, KY
    What Pin_Head is saying is the White/Green wire will have +12 volts on it if the regulator is working and trying to charge the battery.

    Don't overlook the obvious things like a blown fuse... ;)
  11. Lukedog

    Lukedog

    Messages:
    7
    Thats not what i'm getting.... and have checked fuses and wires. the white green or F pin on alternator is like a ground, when i check it from positive it completes circuit, and when i put 12v+ to it it makes a spark.... not good sign... thats what i'm trying to figure out.. Maybe my new alternator is shorted?

  12. Lukedog

    Lukedog

    Messages:
    7
    I ran a new hot wire ( accessory ) to the voltage regulator on black yellow, and now its charging just like its suppose to, i evidentally have a short somewhere in the old one, which i'll be looking for . thanks for the advise and wisdom.

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