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Thread: No power to ignition coil. Might be bad fuse box?

  1. #1
    Join Date
    May 2017
    Posts
    10

    Default No power to ignition coil. Might be bad fuse box?

    Troubleshooting a no spark / won’t start issue on my ‘68 IIa’.

    The starter cranks when I attempt to start the ruck but it will not start. I tested with a spark tester at the plugs and the coil lead - no spark. (New ignition switch)

    I then tested the power to the positive connector on the coil. (New coil). I tested following instructions to have the ignition switch in the on but not cranking position. I tested with a voltmeter when points open - looking for ~12 volts got 0. Also tested with points closed - loving for between 6 and 8 volts got 0.

    I then tested the fuse box using a test lamp. Using the negative battery post for the ground.

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    When I test at the fuse with the ignition off and key out the lamp lights only on the top connected fuse. It also lit when testing at the spade connectors on either side of the fuse. I believe this position is connected to the lights since they work without needing to have the ignition switched on.

    When I Conduct the same tests with the ignition in the on position I the tester lights on all connected fuses. When I test at the spade connectors the lamp only lights on the top and bottom connected fuses. The center position does not light at the connector - only at the fuse.

    I assume this this means that my fuse box needs to be replaced.

    I believe that this fuse box is actually a Series III box based on review of the parts listed by our hosts.

    I thought I’d check with the experts here before I buy this part only to find that 1) I have been testing incorrectly, or ) there are other potential causes for the lack of power to the coil and the failed test at the fuse box.

    Any advice would be greatly appreciated.

    Thanks

    Wes

  2. #2
    Join Date
    Apr 2008
    Location
    The Granite State (NH)
    Posts
    3,456

    Default

    Wes, It'd be helpful if you said whether yours is a + earth or a - earth vehicle; I'm not sure where the changeover to negative earth vehicles occurred, and I'm too lazy to check, so I'll write this as if you have a negative earth land rover...

    Refer to the bottom wiring diagram: https://www.roversnorth.com/files/Im.../LR-page83.pdf



    The primary circuit to the coil (the small wires) don't run through a fuse if the vehicle is still wired the way the factory wired it. It taps into the electricity before it passes through the fuse (on the "upstream" or "supply" side of the fuse). Looking at your picture, this seems to be the case still.


    WITH THE IGNITION SWITCH IN THE "RUN" POSITION (you didn't note this in your procedure), you should have about 12v at the white wire feeding the coil ("+" terminal). If not, then the problem lies upstream of this, since 12v needs to be here at the coil to make the engine run. The troubleshooting method will be to check for 12v at each point upstream on the circuit until you find 12v with the key in the run position, so check for 12v at the other end of the primary wire to the coil, where it (should) be plugged into the fuse panel. Check for 12v where the white wire that supplies the fuse panel plugs into the ignition switch.

    As a side note, if the fuse panel is being supplied properly by the ignition switch via the white wire, the low oil pressure light should be on when you turn the key to the run position. If it isn't, I'd investigate the ignition switch and its wiring (negative earth vehicles).

    Again, presuming you have a negative-earth vehicle where you crank the engine using the keyswitch (not a separate starter button on the bulkhead), then you can presume the ignition switch itself is being supplied properly with electricity, since the starter cranks.

    IF THE WHITE WIRE IS ON THE WRONG TERMINAL POST ON THE IGNITION SWITCH, the truck may not start--It has to be on the terminal post that is "hot" in BOTH the "run" position and the "crank" position.

    Just use the wiring diagram, starting with the coil (it's item #45 on the negative-earth diagram) and work your way backwards to the ignition switch (#23), checking for 12v. Poor connections at the terminals can cause the electricity to stop flowing. Same with broken wires.

    Assuming yours is a negative earth vehicle AND YOU DID HAVE THE IGNITION SWITCH IN THE "RUN" POSITION when testing for power at the coil, my guess would be that the ignition switch is either incorrectly wired, or bad. We can discuss testing the ignition switch if necessary.

    If you DIDN'T have the ignition switch on during the test and 12v really DOES exist at the + terminal on the coil, then the problem likely lies beneath the distributor cap or in the small wire from the coil to the distributor, which we can further discuss.
    Last edited by SafeAirOne; Yesterday at 06:51 AM.
    --Mark

    1973 SIII 109 RHD 2.5NA Diesel

    0-54mph in just under 11.5 minutes
    (9.7 minutes now that she's a 3-door).

  3. #3
    Join Date
    Apr 2008
    Location
    The Granite State (NH)
    Posts
    3,456

    Default

    I re-read your post. Looks like you've done much of what I've suggested already.

    When you say "When I Conduct the same tests with the ignition in the on position I the tester lights on all connected fuses. When I test at the spade connectors the lamp only lights on the top and bottom connected fuses. The center position does not light at the connector - only at the fuse." what do you mean?:

    1) On which side of the fuse is your test lamp lighting? (it should be BOTH sides of the fuse if the fuse is good)

    2) Are you not getting power on the spade terminal post with the GREEN wires or the terminal with the WHITE wires on that 3rd fuse down from the top? (the green side is irrelevant to your starting issue. Only the white side matters)

    3) Are you testing at the terminal POSTS on the fuse panel, or the spade CONNECTORS on the end of the wires?

    You are correct that the brown wire feeding the top fuse should always be "hot" with 12v. The white wires on the two lower fuses should be "hot" with the ignition switch in both the "run" position and the "crank" position. If they do not have 12v in BOTH positions of the ignition switch, then the engine won't start.

    If the SIIA is anything like the SIII, then I believe there is also an "accessory" terminal post on the key switch which ONLY supplies electricity in the "run" position and NOT the "crank" position. This terminal is used to supply accessories that you don't want to power while you're cranking, such as a radio. Make sure your white wire is not plugged into this unused extra terminal post on the ignition switch.


    One last note...The fuse panel is a VERY simple device. A few bent strips of metal and a plastic holder for the strips of bent metal. There's not much to it that can fail. Presuming there's good metal-to-metal contact between the spade terminals and good contact between the fuses and their terminal clips, it's somewhat unlikely that the fuse panel is your culprit.
    Last edited by SafeAirOne; Yesterday at 06:37 AM.
    --Mark

    1973 SIII 109 RHD 2.5NA Diesel

    0-54mph in just under 11.5 minutes
    (9.7 minutes now that she's a 3-door).

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