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  1. #1
    CB750 Enthusiast raywilson's Avatar
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    Tail light wiring woes

    It's been a while since this thread was tapped into. I have a 76 CB750 SS that I've put a new/used harness in because the PO had modified a lot of the functions and clipped a bunch of wires. Tail light won't come on. The Brown tail light wire runs to the new ignition switch and there's 2 browns leaving the switch. They seem intact but I will reluctantly cut the factory plastic to make sure they are connected. The tail light will come on in park and the brake lights work. The speedo/tach lights come on with the turn signals, I think that will be a more logical fix. The tail light is baffling me. All the dash lights work/function but the neutral is always on. Turn signal lights aren't connected yet as I am waiting for my fleabay purchase to arrive. All the colors are connected correctly. I'm assuming the green wire is a common non-specific ground and it doesn't matter what green goes in there. There is a solid lime green wire that isn't shown as lime in the schematic, only one color solid medium green is shown. Thanks in advance for any advice.

    Ray

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  2. #2
    CB750 Enthusiast mrtelec's Avatar
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    check all 3 of your fuses to see if you have voltage there. On my 78 there is a jumper that goes from a black to a brown/ blue I think that ran back to the 1 fuse and fed the running light. I checked with my volt ohmmeter which wire went from the headlight bucket to the fuse panel. the jumper is made of a piece of wire about 3 inches long with bullet connectors, you may want to see if the jumper is still attached to the old harness. I put a new harness on mine along with new blade fuse panel and pulled my hair out until I found it on the wiring diagram

  3. #3
    CB750 Enthusiast raywilson's Avatar
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    Quote Originally Posted by mrtelec View Post
    check all 3 of your fuses to see if you have voltage there. On my 78 there is a jumper that goes from a black to a brown/ blue I think that ran back to the 1 fuse and fed the running light. I checked with my volt ohmmeter which wire went from the headlight bucket to the fuse panel. the jumper is made of a piece of wire about 3 inches long with bullet connectors, you may want to see if the jumper is still attached to the old harness. I put a new harness on mine along with new blade fuse panel and pulled my hair out until I found it on the wiring diagram
    Thanks. I will do that this weekend. I think I'm gonna have to strip the tape /plastic off the new harness to see what's really there. The bad must be buried in there. The only cut wire I found in the harness is that light green one that doesn't show up on the wiring schematic anyway

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  4. #4
    CB750 Enthusiast raywilson's Avatar
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    Quote Originally Posted by raywilson View Post
    Thanks. I will do that this weekend. I think I'm gonna have to strip the tape /plastic off the new harness to see what's really there. The bad must be buried in there. The only cut wire I found in the harness is that light green one that doesn't show up on the wiring schematic anyway

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    On my 76 the tail light wiring is brown but it has the junction that you described. I opened up the plastic wire casing around the harness and the connection is clean and tight. Continuity is strong from the taillight to the 2 brown wires at the key. I noticed tonight that when I push the blinkers on, the taillight comes on, slightly fainter than normal. The taillight comes on in park. Bad switch?? That's where I'm going now, new switch. Ideas??

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  5. #5
    CB750 Addict Chris in Dorset England's Avatar
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    Hi,
    The dim tail light is current seeking a ground other than the correct one. Check ALL the grounds for cleanliness and tightness and continuity. I have seen car headlights come on when the brakes are used, cause, no ground for the brake lights, the current found a ground through the head lights!
    Last edited by Chris in Dorset England; 03-09-2018 at 06:58 AM. Reason: more info

  6. #6
    CB750 Enthusiast mrtelec's Avatar
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    I agree with Chris, it seems there is a dirty connection or bad ground, have you installed the turn signals that you were waiting for? Check the wire bullet connectors, light sockets and turn signal switch for poor or bad connections


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  7. #7
    CB750 Enthusiast mrtelec's Avatar
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    Quote Originally Posted by raywilson View Post
    All the dash lights work/function but the neutral is always on. Turn signal lights aren't connected yet as I am waiting for my fleabay purchase to arrive. All the colors are connected correctly. I'm assuming the green wire is a common non-specific ground and it doesn't matter what green goes in there. There is a solid lime green wire that isn't shown as lime in the schematic,
    The neutral light stays on even if you put it in gear? The neutral switch light has a green with red tracer and black wires going to it. Is it connected to the green with red tracer or could it be to a green? if you follow the green/red wire from the neutral light it is also in the circuit from the clutch switch leading to the starter solenoid, may want to check those connections also.
    Last edited by mrtelec; 03-09-2018 at 05:03 PM.

  8. #8
    CB750 Enthusiast raywilson's Avatar
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    Quote Originally Posted by mrtelec View Post
    The neutral light stays on even if you put it in gear? The neutral switch light has a green with red tracer and black wires going to it. Is it connected to the green with red tracer or could it be to a green? if you follow the green/red wire from the neutral light it is also in the circuit from the clutch switch leading to the starter solenoid, may want to check those connections also.
    Ya, the neutral light is still on, light gr w red. Doesn't affect anything yet. Followed it back, maybe the switch is bad? Front and rear blinkers work/flash, brake lights front and rear work, headlight H/L work. Taillight works well on park, doesn't on running. I have 2 brown w blue stripe wires coming from the harness. The one I have connected to the switch has a white marker that corresponds with the one from the harness. So one is not used. Fuses are good. Tach and speedo lights don't come on but they would earlier when the blinker was on.
    All connections seem tight and clean. They are hard to push together so there's good contact. It's a head scratcher...


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  9. #9
    CB750 Enthusiast raywilson's Avatar
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    Quote Originally Posted by raywilson View Post
    Ya, the neutral light is still on, light gr w red. Doesn't affect anything yet. Followed it back, maybe the switch is bad? Front and rear blinkers work/flash, brake lights front and rear work, headlight H/L work. Taillight works well on park, doesn't on running. I have 2 brown w blue stripe wires coming from the harness. The one I have connected to the switch has a white marker that corresponds with the one from the harness. So one is not used. Fuses are good. Tach and speedo lights don't come on but they would earlier when the blinker was on.
    All connections seem tight and clean. They are hard to push together so there's good contact. It's a head scratcher...


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    I did get a new ignition from cb750 supply and I replaced the RH switch with new. I have new LH coming. It's an old bike and new switches take some electrical mystery away. I haven't checked the charging circuit yet. I've only ridden it about 50ft, the old brakes didn't do much and was a bit scary. Put new pads in so that should help there.

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  10. #10
    CB750 Enthusiast mrtelec's Avatar
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    Quote Originally Posted by raywilson View Post
    Front and rear blinkers work/flash, brake lights front and rear work, headlight H/L work.
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    when you hit the turn signal does the buzzer buzz and where are the 2 wires from that go to? one is brown/blue and the other black.in your pictures I don't see the buzzer .. could it be that you have the brown/blue in the wrong connector. Is there any open black connectors up front also? Do you have the old harness still? if so look at the black connector and see if there is a connection from the black to a brown or brown/blue

    Quote Originally Posted by raywilson View Post
    Front and rear blinkers work/flash, brake lights front and rear work, headlight H/L work.
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    " Brake lights front and rear"?( did you mean front brake lever and rear foot switch ) should only be rear tail light that comes on. the brake switches give the power to the tail on the green/yellow wire and the light gets grounded by the green wire. Tach and speedo lights have 2 wires each to them the brown/white and green. Do you have a volt/ohmeter to check the br/white wires for the 12v? all three fuses have 12 volts at them? I know I'm probably telling you everything you already know but I can't see it myself so I'm running these things by you

  11. #11
    CB750 Enthusiast raywilson's Avatar
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    Quote Originally Posted by mrtelec View Post
    when you hit the turn signal does the buzzer buzz and where are the 2 wires from that go to? one is brown/blue and the other black.in your pictures I don't see the buzzer .. could it be that you have the brown/blue in the wrong connector. Is there any open black connectors up front also? Do you have the old harness still? if so look at the black connector and see if there is a connection from the black to a brown or brown/blue




    " Brake lights front and rear"?( did you mean front brake lever and rear foot switch ) should only be rear tail light that comes on. the brake switches give the power to the tail on the green/yellow wire and the light gets grounded by the green wire. Tach and speedo lights have 2 wires each to them the brown/white and green. Do you have a volt/ohmeter to check the br/white wires for the 12v? all three fuses have 12 volts at them? I know I'm probably telling you everything you already know but I can't see it myself so I'm running these things by you
    I'll check it out your suggestions today. You say the the front hand brake shouldn't make the brake light go on? I remember seeing the wire coding for the blinker buzzer, I don't have it connected to anything. But I will recheck everything w your suggestions this afternoon. Thank you, I'll let you know...


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  12. #12
    CB750 Enthusiast mrtelec's Avatar
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    Both hand brake and foot brake light tail light.

  13. #13
    CB750 Enthusiast raywilson's Avatar
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    Quote Originally Posted by mrtelec View Post
    Both hand brake and foot brake light tail light.
    Okay, instead of checking continuity I checked voltage. Sorry about that lameness. Only 2 fuses getting 12v. No power to taillight but there's power when in park. So I guess it's a bad LH switch? Or the new ignition is defective?

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  14. #14
    CB750 Enthusiast mrtelec's Avatar
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    No, you need a jumper wire from a 3 or 4 black 4 way connector to the brown blue wire that feeds the fuse that is not powered. If you can't find it on the old harness then make 1 out of a 3 inch piece of wire with 2 male bullet connectors. To find which wire is the right 1 then you want to use your ohmeter to see which wire feeds the fuse

  15. #15
    CB750 Enthusiast raywilson's Avatar
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    Quote Originally Posted by mrtelec View Post
    No, you need a jumper wire from a 3 or 4 black 4 way connector to the brown blue wire that feeds the fuse that is not powered. If you can't find it on the old harness then make 1 out of a 3 inch piece of wire with 2 male bullet connectors. To find which wire is the right 1 then you want to use your ohmeter to see which wire feeds the fuse
    I kinda tried that but I will trace the brown blue to the fuse and run a jumper. Thanks again.

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  16. #16
    CB750 Enthusiast raywilson's Avatar
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    Quote Originally Posted by raywilson View Post
    I kinda tried that but I will trace the brown blue to the fuse and run a jumper. Thanks again.

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    With the jumper there's equal readings to all 3 fuses. Rear Light does not go on. Parking still works, different circuit. There is no power in the solid brown wires at the new ignition switch which goes to the rear light. I checked where the browns connect and have the factory solder and it's clean and tight. Everything else works. I think even the signal buzzer would work but it's blown. I think my new switch is at fault. I have used switch but no key. I'll try to get a key made and see if that fixes it.

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  17. #17
    CB750 Guru amc49's Avatar
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    Not correct, by that '76 schematic you CANNOT have power at all 3 fuses yet none at browns at ignition switch key on position 1 as one of those browns is the one that supplies at least the taillight fuse. No power at the ignition switch browns means at least one fuse needs to be be dead, or bike is miswired or shorted harness.

    I'm having trouble anyway with where you are going, any brown/blue wire is headlight only and jumps nowhere in that run, it either runs to headlight switch as already powered past the fuse or to starter switch to hit black and pick up power there. If you are following the schematic anyway. None of that is going to fix the taillight.

    At some points the schematic colors are vague, hard to see brown/blue in there but taillight is definitely brown only.

    There should be a brown/white wire in the bundle connector that attaches to the ignition switch, verify that.
    Last edited by amc49; 03-11-2018 at 11:52 PM.

  18. #18
    CB750 Enthusiast mrtelec's Avatar
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    amc in the new harness that they sent me the break down for the wires at the fuses were 2 browns that were for the main (one in and the other out) 2 brown with red tracer for the headlight (1 in 1 out side of fuse ) for headlight and the last pair at the fuses was the Brown blue wires, which went to the tail light, the schematic is def vague. but yes the tail light wire for the tail light is brown. somewhere it gets from the brown/bl to the brown I haven't looked at where in the harness yet.


    ray I would check the fuse to make sure it isn't blown then check the brown hot wire and green ground wire at the tail light and see if you have 12v there, if you do it could be the socket.

  19. #19
    CB750 Guru amc49's Avatar
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    So wiring harnesses not correct as to color code..............great. I absolutely would not be buying from that person at all.

    The wire colors of course do not matter other than making things easier to understand, but you still have to make sense of the schematic. A quick check of the fuse values will sort them out at fuses, each being a different amp. The only thing vague about the schematic is a few of the wire colors and with a harness in hand it would still be simple to figure them out. And of course once you commit to which color you use for what you must get those to the correct place in the schematic.

    You should have no power at the green wire in taillight it being a ground, unless shorted. Power will be on the green/yellow with brake on.

    If for the sake of discussion the taillight wire in harness is brown/blue, then there must be one at ignition connector and one way back at end of harness over top of rear fender.
    Last edited by amc49; 03-12-2018 at 03:24 AM.

  20. #20
    CB750 Enthusiast mrtelec's Avatar
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    It gets better, there are 2 br/bl wires in the head light too, one is from the turn signal switch that goes to the turn signal buzzer. That's where he had the original problem where his tail light came on with the turn signals, he had the brown blue going to the fuse connected to the turn signal br/bl out of the turn signal switch. And yes you need to make sure you have the right wire that goes into the fuse. That's where I used the ohmeter to see which wire went to the fuse. By jumping it to the black it comes on with the switch.
    Last edited by mrtelec; 03-12-2018 at 10:14 AM.

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