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Thread: M25 Glow Plugs Blowing Fuse

  1. #1
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    M25 Glow Plugs Blowing Fuse

    Hi all. I have just completed the alternator bracket upgrade after having a bolt holding the old bracket shear off in the block and having to drill and re-tap that on the way to a cross Lake Michigan race. Felt I was probably living on borrowed time. Does anybody need the old style bracket? Did very well on the race but now I am having trouble with blowing fuses every time I hold in the glow plug button for about 5 seconds.

    We upgraded to Main Sails favorite Leece Neville 90 amp alternator, taped off the exciter wire as it is not needed with the new alternator, and grounded the alternator from the block to the negative post on the alternator as this is needed. I think we have grounded everything correctly.

    Turn the key....fuel pump kicks in, (will run as long as you need without blowing fuse) press glow pug button and after 2-5 seconds this blows the 15 amp in-line fuse from the battery cable at the starter switch. This fuse has been fine for 2 years now.

    What could have changed with my new alternator installation or did a glow plug just pack it in coincidentally with this upgrade? Didn't change any wiring other than the alternator and I did lead all the grounds on the exhaust manifold to a single bus bar.

    Yes the glow plug upgrade is next on my list.

    Doug

  2. #2
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    A re you sure you are on a 15 amp fuse? These glow plugs draw about 13 amps each. That's 36 amps of draw at 11.5 volts. The electrical systems on these engines were pretty mickey mouse to begin with and owner mods since then don't help. There was no fuse in the system that I could find before I ripped out my system and started over. I currently have a heavy duty relay and a heavy duty 50 amp fuse for the glow plugs. that way, I am not routinely sending 40 amps through the starter switch, glow plug switch and starter switch. Also, my run from batteries to glow plugs is 3' from the batteries instead of the 30' I had before with that awful trailer plug system before. The result is much higher voltages at the glow plugs.

    I also have the same alternator. It is working great but it came with no instructions. Also, mine is optimized for AGM batteries. No problem as that. is what I have but the manufacturer indicated you need a separate regulator if you use flooded cells.
    Last edited by supersailor; 07-16-2017 at 06:03 PM.
    Bob Morrison
    1987 E-34 Hull #15
    "Terra Nova"

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    Just did the alternator bracket mod this winter, but I kept the original 50 A Motorola alternator (the regulator uses the purple, key-switched exciter wire). I also had to re-route the grounds from the exhaust manifold to a ground bus bar.

    Just to clarify: Is the in-line fuse that is tripping in the yellow/red wire to the starter solenoid? I don't think my grey/blue glow-plug wire has an in-line fuse. Or, are you talking about the red wire with the in-line fuse that is located behind the engine panel? (runs between the old ammeter/battery hot lead and the key switch).

    Also, I think the M-25 manual says the glow-plugs are 7 A each, or 21 amp for a 3 cyl M-25. If your re-grounding increased current flow, now maybe you are getting the full 20+ amp draw from the glow plugs. Maybe try a 20 A fuse?
    Last edited by Kenneth K; 07-17-2017 at 10:59 AM.
    Ken
    '85 E32-3 "Mariah" #641

    "Saltwater is the cure; sweat, tears, or the sea......"

  4. #4
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    The alternator change and the glow plug button should not affect the starter solenoid circuit except to drop the voltage to the solenoid. You can use a clamp on type current tester to see the current draw at each circuit. The solenoid should not draw anywhere close to 15 amps. There is a wiring fault somewhere here. The original wiring with all the circuits coming through the ammeter and the ignition switch actually is dangerous. If you still have the trailer harness, pay attention to Mainsails excellent article on why you should dump it immediately. I know Loren Beach has grounded his boat because his trailer connectors are running 10 degrees hotter than the rest of his harness on a thermal imager.
    Bob Morrison
    1987 E-34 Hull #15
    "Terra Nova"

  5. #5
    Principal Partner Tom Metzger's Avatar
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    If all else fails, get out the manual. The manual calls for a 20 amp fuse to the solenoid (yellow/red wire) and a 30 amp fuse for the engine panel (behind the panel (red wire). It also shows 6 amps/glow plug.

    Since the 15 amp fuse blows after the glow plugs have been energized for a while that would indicate that the current is only a little above the fuse rating and the larger fuse will do the job.

    That said, I don't think you are wired according to the wiring diagram because the glow plugs should not be in the solenoid coil circuit. If the yellow/red wire connects to the battery cable it shouldn't go to the glow plug switch. I'd check it out against the wiring diagram. The y/r wire is #16 which is too small for a the power feed to the engine.
    Tom Metzger
    E-34 Xanthus

  6. #6
    Senior Moderator Loren Beach's Avatar
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    Electircal

    Quote Originally Posted by Tom Metzger View Post
    If all else fails, get out the manual. The manual calls for a 20 amp fuse to the solenoid (yellow/red wire) and a 30 amp fuse for the engine panel (behind the panel (red wire). It also shows 6 amps/glow plug.

    Since the 15 amp fuse blows after the glow plugs have been energized for a while that would indicate that the current is only a little above the fuse rating and the larger fuse will do the job.

    That said, I don't think you are wired according to the wiring diagram because the glow plugs should not be in the solenoid coil circuit. If the yellow/red wire connects to the battery cable it shouldn't go to the glow plug switch. I'd check it out against the wiring diagram. The y/r wire is #16 which is too small for a the power feed to the engine.
    There is also another possible complication. I found that our engine panel wiring was changed when the PO removed the key switch and put a simple on-off switch in place of it. Our glow plug circuit is, however, separate from the stater button, along with a disturbing number of multi-wire crimp splices in that area.
    All of this is about to get changed out, due to evidence of resistance in the two 'trailer plugs' in the original harness.
    (I will probably base our upgrade on much Bob's M25XP wiring upgrade when doing this change. His addition of the Blue Seas fuse panel by the original boat cockpit panel backside is neatly done.)
    Last edited by Loren Beach; 07-20-2017 at 11:02 AM.
    1988 Olson 34 #8
    Sail # 28400
    Universal M25XP
    Fresh Air
    Portland, OR USA

  7. #7
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    Well I found the original fuse in the larger red intstrument panel wire was 30 amps

    And it just might have been old and it was an AGC Quick-Blow. Then I replaced it with an assortment of fuses that were 15 to 20 amp because those were what I had and I couldn't find my reading glasses. (or magnifier hood)

    I have now replaced the fuse with a slow-blow MDL 30 amp fuse and things seem to be working fine. I did replace the glow pugs too however so I am not quite sure which change did the trick. The glow plugs were easy once I got the intake manifold off.

    The solenoid for the glow-plug circuit just arrived and I will be hooking that up over the next week.

    Doug

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