84 CB450SC Headlight doesn't work
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  1. #1
    Senior Member BlargKing's Avatar
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    84 CB450SC Headlight doesn't work

    Hello,

    Like the title says, I just got a used CB450 and every works great, except Ive got no high or low beam headlight. I checked the bulb with my multimeter and theres continuity on both filaments so the bulb is good, and checking with my multimeter Im not getting power at the bulb socket or at the switch on the handlebars, so the problem must be before those components. Im going to assume theres a fuse and/or relay that controls the headlight, so my next step would be to check those out, but Im not sure where to look for them. I checked under the seat and near the battery to no avail, so I thought I would ask if someone knows where to look before I keep pulling off random panels.

    Thanks!

  2. #2
    Senior Member 80cb400t's Avatar
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    The 450sc might be different but on all the cb400s the fuse panel is under the left side cover
    1980 CB400T - 1 running, 1 parts bike
    1965 CB160 - 1 kind of running, 1 parts bike

  3. #3
    Member mikemo's Avatar
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    Check for +12 volts at the headlight fuse. The fuses are under the left side cover. If you don't have +12 volts on both sides of the fuse, then it could be the starter switch (or another wiring issue).
    Good luck.

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  5. #4
    Senior Member BlargKing's Avatar
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    Got the side panel off where the fuses are, turns out it was just a blown fuse. Got a new fuse in and my headlight works, though those old sealed beams are pretty dim.

    One side effect is it seems with the headlight working theres a lot less power getting to the battery. The battery died on me even after riding for half an hour. Probably going to replace the rectifier/regulator with one of the new ones, and maybe an LED headlight retrofit.

    Thanks for the help!

  6. #5
    Senior Member 80cb400t's Avatar
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    That sounds like it would be worth first investigating all the connectors and wires connected to that fuse. Maybe the reason the battery isn't getting charged is that there's a rusty connection taking the energy away from the battery and dissipating it as heat.

    Without a multimeter test showing failure I'd probably trust the 40 year old reg/rec that was made to Honda standards over anything that doesn't cost more than a tenth of what the bike is worth.
    Last edited by 80cb400t; 08-21-2019 at 07:33 PM.
    1980 CB400T - 1 running, 1 parts bike
    1965 CB160 - 1 kind of running, 1 parts bike

  7. #6
    Super Moderator longdistancerider's Avatar
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    Moved to SOHC Electrical
    Good you found the problem and fixed it. Now did you use SAE fuses or metric ones? SAE are too long so you only get partial contact on the brass holders, those need to be sanded bright and shiny, which results in the fuse block melting due to heat.
    You need the FSM, Factory Service Manual. PM sent
    Last edited by longdistancerider; 08-21-2019 at 08:01 PM.
    Jim O'Brien
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