78 CM185T Electrical Issues - rectifier maybe?
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Thread: 78 CM185T Electrical Issues - rectifier maybe?

  1. #1
    Junior Member rileyc13's Avatar
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    78 CM185T Electrical Issues - rectifier maybe?

    I just bought this 78 CM185T this week. I drove it around before buying it and everything was great. I didn't have any issues driving it around that day. But at night I realized the headlight didn't turn on when I started the bike. I had to switch on the Hi-beam for the light to come on. Then I noticed the blinkers didn't blink, but were just solid. I tried the horn and found that it didn't work.

    78 CM185T Electrical Issues - rectifier maybe?-img_3184.jpg

    I have done some checks with a multimeter to try and diagnose the issue.

    Stator: I checked the connector and had continuity between the Pink, White and Yellow wires.
    Rectifier: This one was pretty weird. The FSM has a diagram of which wires to test and the polarity. Testing the Red and Pink wires didn't give me the continuity beep but the multimeter read 543 Ohms. I got 547 Ohms when I tested Red and Yellow, again no beep. The third set, Red and Green was Open Line. The Pink and Green had no beep and 547 Ohms. And the Yellow and Green was Open Line.
    Attachment 290502

    If I am interpreting these results right, then my rectifier is definitely bad right?

    I decided to pull off the headlight and test the other connectors. I followed the FSM charts for these too.

    Ignition Switch: With the key in the off position, I shouldn't get continuity between any of the leads. But I got continuity between Black and Brown/White. I also got continuity with Red if the negative probe was on it and the other on Black or Brown/White. With the key in the middle ON position, all the leads should have had continuity. But Brown had no continuity.
    Attachment 290504
    So my ignition switch is also bad?

    Turn Signal: According to the FSM chart, only certain wires should have had continuity depending on where the turn signal switch was located. Regardless of the switch, I got continuity between them all.
    The turn signal is busted too?

    Engine Stop Switch: With the switch in OFF position, there should have been no continuity but there was.


    So in conclusion, is nearly everything electrical on this bike messed up? Are all these issues caused by one fault? I'm pretty new to this business so did I do these tests wrong?

    Hopefully someone else has had issues like this before.

  2. #2
    Sensei 66Sprint's Avatar
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    You are performing irrelevant tests, as the rectifier has polarity that must be considered, and ALL the lighting is ultimately connected by a common ground....
    You are close enough to phone me and I'll be happy to guide you through the correct tests....540-525-5199......

    Make sure your battery is fully charged, you have a multimeter, and basic hand tools handy.....
    Last edited by 66Sprint; 09-12-2019 at 10:09 PM.
    "I have a mind like a steel trap.....Old and rusty, of antiquated design, and hard to get stuff back out of...."
    Contact info: E-mail; [email protected] Phone; 540-525-5199

  3. #3
    Junior Member rileyc13's Avatar
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    Thanks for the help 66Sprint. I spent a while cleaning the electrical contacts in the headlight area and under the seat last night. The headlight is working much better now and now the horn works! The blinkers still don't blink unless I am at a high rpm but at least there is some progress.

    I noticed some funny wiring under the seat though. There is an orange wire that is connecting the black wire on the blinker relay to a brown wire that I believe connects to the tail light. In the picture you can see that someone taped the orange wire to the black one. You can also see the brown wire that was connected to it and at the very bottom the other end of the brown wire that should have been connected. The orange wire is a female spade connector and the brown one is a male bullet connector, so they are clearly not meant to connect. If my description is confusing, take a look at the wiring diagram that I colored.

    Anyone know why the previous owner did this?

    78 CM185T Electrical Issues - rectifier maybe?-img_3205.jpg
    78 CM185T Electrical Issues - rectifier maybe?-weirdwires.jpg

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  5. #4
    Sensei 66Sprint's Avatar
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    That was likely done so the taillight would come on because according to your tests, the ignition switch does not make the brown/white to brown connection....
    Phone again, and I'll explain further, but you will have to post the results for the group....
    Last edited by 66Sprint; 09-14-2019 at 10:41 AM.
    "I have a mind like a steel trap.....Old and rusty, of antiquated design, and hard to get stuff back out of...."
    Contact info: E-mail; [email protected] Phone; 540-525-5199

  6. #5
    Junior Member rileyc13's Avatar
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    Update: After talking with 66Sprint, I tested the alternator and the battery with a multimeter. I unplugged the alternator and jumped the blue wire back to the wiring harness then measured the AC voltage across the pink and yellow wires and the pink and white wires. Across one I measured about 6 volts at idle and revved it up above 50V. The other was about the same but above 40V.

    Then I tested the DC voltage at the battery as I revved the bike. It never read higher than 6V no matter how high I revved the bike.

    So I'm thinking I need a new rectifier. Any ideas of where I should get one?
    Or did I do this all wrong? Because that is definitely possible.

  7. #6
    Sensei 66Sprint's Avatar
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    You did the test correctly, and your alternator appears to be fine......
    (although I would be interested in knowing the approximate revs or throttle positions where the AC output was 18 VAC and 25 VAC)

    It DOES appear that you need a new rectifier/regulator unit........
    "I have a mind like a steel trap.....Old and rusty, of antiquated design, and hard to get stuff back out of...."
    Contact info: E-mail; [email protected] Phone; 540-525-5199

  8. #7
    Super Moderator ancientdad's Avatar
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    ^^^and what Steve means specifically is to replace the rectifier (and separate regulator if the bike has one) with a modern rectifier/regulator combo unit. One of our sponsors happens to sell the best combo unit for as good a price as you'll find as compared to all the other units available out there, and backs it up with plenty of support here from the owner himself (HT member Sonreir).
    Tom

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  9. #8
    Sensei 66Sprint's Avatar
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    Tom,
    Member will have to contact Matt directly, as this is a 6 Volt system.....
    "I have a mind like a steel trap.....Old and rusty, of antiquated design, and hard to get stuff back out of...."
    Contact info: E-mail; [email protected] Phone; 540-525-5199

  10. #9
    Super Moderator ancientdad's Avatar
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    Quote Originally Posted by 66Sprint View Post
    Tom,
    Member will have to contact Matt directly, as this is a 6 Volt system.....
    Yes - I knew Matt had one available though probably not on his website, so I provided Matt's profile link to help him easily get in touch with him
    Tom

    CL450 project reboot, street legal this time

    Budget drag bike project

    Ride along at the drag strip



    running points... because I'm too old for mysteries that begin with pushing

  11. #10
    Junior Member rileyc13's Avatar
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    I contacted Matt about the 6v rectifier. Thanks for the help guys!

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