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Discussion Starter · #1 ·
Hey all,

I have a 1974 Honda CB125s that starts nicely and runs well. But I do have some electrical problems. The high beam headlight, horn, neutral light, and brake light are all working. But for the life of me I cannot get the blinkers to work: none of the four blinkers are working. Checked the bulbs and everything. The low beam headlight isn't working either but I assume that's just the bulb.

I have a multimeter but am really inexperienced/intimidated by electrical work. Not really sure the best place to start and any help would be appreciated. Wiring diagram is attached.

Thanks to all in advance! I need to fix this before I can get it on the road.
Technical drawing Plan Diagram Drawing Parallel
 

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Just follow the power. Unplug the winker relay, and check for battery Voltage (~12.6V) on the black (Bk) wire with the main switch ON. Don't be slow, as you can burn a coil if it is powered on with the contact breaker closed for too long. If that is good, plug the relay back in and open the bullet connector that the grey (Gr) wire passes through, repeat power test. Next, that pile of connectors left of center should be in the headlamp bucket; find the Gr wire and repeat power test. Then find the LB or O wire connectors and, with the turn switch in the right position find power at LB, left position O. From there, the wire colors change, but you can remove the bulbs and test at the center contact of the bulb sockets. Odds are, one or more of the Gr or Bk bullet connectors are not connected well, probably from age. The same could be true of the White (W) wire bullet to the low beam.
 

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Discussion Starter · #3 ·
I think I've got it @WintrSol. I think it's the winker relay. I've got a new one coming tomorrow. The old one was rusted to hell and I wasn't getting continuity across the two leads of it because of the corrosion. I was confused though because most forums said that it's usually only the winker relay if the lights go on but don't blink. Mine weren't going on at all, but that'd make sense if the winker relay wasn't letting the circuit close. At least I think I'm right, because the blinker switch seems fine. I'll keep you posted!
 

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2006 Honda CBR1000RR, 2008 Honda CRF230L, 2019 Honda CRF1000L
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I think it's the winker relay.
Ayup, those will always mess up. On a 74, make sure you check and adjust as needed, your carburetor chain, top off the blinker(winker?) Fluid and get that knueter valve adjusted!

🤭
 

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Cute, but that's what it says on the diagram, so I just went with it, so as not to confuse anyone.
The relay could actually be good, inside, but if it is so corroded it won't pass current, it's not worth cleaning up.
 

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Cute, but that's what it says on the diagram, so I just went with it, so as not to confuse anyone.
The relay could actually be good, inside, but if it is so corroded it won't pass current, it's not worth cleaning up.
Hope that's what his problem is because I thought current always got thru but if the resistor inside was corroded it couldn't break clear to start the blinking. I suppose it could be so rusted and corroded that the resistor is just gone though. That would certainly show no continuity. They are cheap enough to just replace just to rule it out no matter what though. But do hope this is the problem and he's soon running down the roads taking advantage of these beautiful early fall weather conditions.
 

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Discussion Starter · #7 ·
That's what I was wondering too @hogcowboy. We'll see today when the new one arrives. I watched one video that said in many flashers the default position is to not let current through, and then when current hits the relay it connects the switch and starts to open and close. My hope is that somehow the relay is stuck open with no current passing through. Other than that I'm not sure what it could be because the switch seems perfectly. fine.
 

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I guess it depends on where the corrosion is. If the contacts on the outside are the problem, then a file to get to bare metal would give you someplace to measure, but if it is also bad on the inside, there's no hope. In any case, unless you like tinkering with stuff, they are cheap to replace.
 

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Just follow the power. Unplug the winker relay, and check for battery Voltage (~12.6V) on the black (Bk) wire with the main switch ON.
Just a note here... This is a 6V bike so you would expect to see something in the area of 7.2 to 6V on the black wire.

Also keep in mind that Honda used BLACK (Bk) for power after the ignition switch. Black is not ground!! Green is in Honda speak!
 

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Discussion Starter · #10 ·
Ok so @RebelnDirt I plugged in the new winker relay but didn't change anything. Then I took the winker relay out, turned the key on and took one of the multimeter leads and put it to ground, and put the other on the black wire. But even with a fully charged battery I was only getting like 1 volt. What could that mean? I was definitely getting some power though. But also both the leads going into the winker relay are pretty corroded. Now I have no idea what to do next. Any help would be really appreciated.
 

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OK so the one volt would be about right considering how electricity works. The winker relay is not the load, so in thinking that the black and grey wires are + and - are a flawed way of thinking about the issue. In this case the black is + and the frame of the bike is - . The grey wire goes to - but after it goes through the switch then the lights then ground (-).

So lets follow the circuit here. Battery - goes right to the frame of the bike. We will get back here in a minute. Battery + comes off as a red (and red/white but we dont worry about this for this example) and the red goes to the ignition switch. When the switch is in the "on" position the + leaves now as a black wire.

For just the blinker circuit, the black wire goes into the winker relay then exits the relay as a grey wire. The grey wire then goes to the blinker switch on the bars. Depending on which direction you choose the wire then leaves that switch as Light Blue (Lb) or Orange (O). That is still a "hot" wire which then goes to the front and rear turn signal light bulbs (these are the load) and from there to ground (See we got back there).

So by reading your meter from the black and grey wires on the winker you will be reading a voltage drop from the entire circuit all the way to the lights. This will also include some extra resistance due to dirt and corrosion.

Reading a schematic in this fashion from battery to load will help you diagnose many issues you will run into. Not all wires are + or - so DON'T ever just assume that. Sometimes assuming that could damage components or even shock you. 6V wont shock you but the capacitor (ie condenser) on the coil can store a voltage even when power is off and if you are not careful it could trigger the coil to fire one more time!! That will zap you pretty good!.

Lemme know if you need anything else.
 

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Ok so @RebelnDirt I plugged in the new winker relay but didn't change anything. Then I took the winker relay out, turned the key on and took one of the multimeter leads and put it to ground, and put the other on the black wire. But even with a fully charged battery I was only getting like 1 volt. What could that mean? I was definitely getting some power though. But also both the leads going into the winker relay are pretty corroded. Now I have no idea what to do next. Any help would be really appreciated.
I forgot this is a 6V system, so many replacement relays won't work; you need one for a 6V system, not a common 12V auto 'winker' relay.

I'm assuming you mean the engine case or battery (-) is ground, not the Gr wire. If so, 1V is a problem. Follow the Bk wire back to the main switch, and test at the bullet connector there. Still 1V, check the R wire back to the fuse at the battery. Old-style fuse holders can get really oxidized and drop the Voltage a lot. Also, the metric size fuze is not the same as US types. The one on my 450 was so old and weak, I replaced it with a modern blade type fuse and holder.
 

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Discussion Starter · #13 ·
OK so the one volt would be about right considering how electricity works. The winker relay is not the load, so in thinking that the black and grey wires are + and - are a flawed way of thinking about the issue. In this case the black is + and the frame of the bike is - . The grey wire goes to - but after it goes through the switch then the lights then ground (-).

So lets follow the circuit here. Battery - goes right to the frame of the bike. We will get back here in a minute. Battery + comes off as a red (and red/white but we dont worry about this for this example) and the red goes to the ignition switch. When the switch is in the "on" position the + leaves now as a black wire.

For just the blinker circuit, the black wire goes into the winker relay then exits the relay as a grey wire. The grey wire then goes to the blinker switch on the bars. Depending on which direction you choose the wire then leaves that switch as Light Blue (Lb) or Orange (O). That is still a "hot" wire which then goes to the front and rear turn signal light bulbs (these are the load) and from there to ground (See we got back there).

So by reading your meter from the black and grey wires on the winker you will be reading a voltage drop from the entire circuit all the way to the lights. This will also include some extra resistance due to dirt and corrosion.

Reading a schematic in this fashion from battery to load will help you diagnose many issues you will run into. Not all wires are + or - so DON'T ever just assume that. Sometimes assuming that could damage components or even shock you. 6V wont shock you but the capacitor (ie condenser) on the coil can store a voltage even when power is off and if you are not careful it could trigger the coil to fire one more time!! That will zap you pretty good!.

Lemme know if you need anything else.

I appreciate this detail. It all makes sense in theory, I'm just not sure what to actually test next. Sorry if I'm being thick headed...if I'm getting a 1v reading on the black wire heading into the winker, that tells me that there is power successfully coming from the ignition coil right? Then the current goes into the winker and out via the grey wire. And the winker relay is brand new, although the original leads are a bit corroded. So it seems the blinker relay isn't the problem.

I've taken the blinker switch at the handlebars apart and it seems totally clean and functional. I guess I should use a multimeter to test voltage coming in there though?

The blinker switch is the last piece in the circuit which all four blinker lights have in common. It's not as if just the right blinkers aren't working, it's all four of them. Which is what made me think its the winker relay or the switch. But I'm not sure what tests to run. I'm new to using a multimeter which I'm sure is part of the problem. I appreciate the help.
 

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Discussion Starter · #14 ·
I forgot this is a 6V system, so many replacement relays won't work; you need one for a 6V system, not a common 12V auto 'winker' relay.

I'm assuming you mean the engine case or battery (-) is ground, not the Gr wire. If so, 1V is a problem. Follow the Bk wire back to the main switch, and test at the bullet connector there. Still 1V, check the R wire back to the fuse at the battery. Old-style fuse holders can get really oxidized and drop the Voltage a lot. Also, the metric size fuze is not the same as US types. The one on my 450 was so old and weak, I replaced it with a modern blade type fuse and holder.
Just saw this. I did get a 6v winker, not a 12v. So we're good on that front. Just to be triple clear at how I'm testing this black wire: I should unplug the winker relay, set my multimeter to Volts, and take one lead and hold it to the black wire, and take the other lead and put it on the negative terminal of the battery or on a grounded bolt on the frame? If so, yes it was reading about 1 volt. I'll do the tests that you mentioned. It would just be weird if the whole system was lacking power though, because the headlight and brake light and neutral light and horn work fine.
 

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Just saw this. I did get a 6v winker, not a 12v. So we're good on that front. Just to be triple clear at how I'm testing this black wire: I should unplug the winker relay, set my multimeter to Volts, and take one lead and hold it to the black wire, and take the other lead and put it on the negative terminal of the battery or on a grounded bolt on the frame? If so, yes it was reading about 1 volt. I'll do the tests that you mentioned. It would just be weird if the whole system was lacking power though, because the headlight and brake light and neutral light and horn work fine.
YES exactly that!!

I didn't mention the coil at all... Re read how I described the circuit path. From the black wire to the - terminal on the battery what is the voltage? It should be the same as the battery + to battery - Thats the key measurement here. If that measurement is 1V then you have a dead battery.
 

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Discussion Starter · #16 ·
YES exactly that!!

I didn't mention the coil at all... Re read how I described the circuit path. From the black wire to the - terminal on the battery what is the voltage? It should be the same as the battery + to battery - Thats the key measurement here. If that measurement is 1V then you have a dead battery.
Ok, I just took the measurement again. The measurement on battery + to battery - is about 6.1v. The measurement from black wire to the - terminal on the battery is 1.15 volts.
 

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Also make sure the volt meter is set to DC volts not AC The icon for AC is usually a squiggle line like this ~ where DC is a solid line _ Or a solid line with dashes above it --- Or it simply says Ac or Dc.

To check if you are getting a complete circuit you could take out a bulb (if you have them) and check DC voltage from the outer shell of the socket to the center terminal. If the winker is installed the voltage will go up and down and be hard to read. Remove the winker, touch the black and grey wires together and then see if the lights come on or check with the meter. It should be at or very close to battery voltage at this point. If not there is a connection issue or corrosion. Honda liked to hide the connectors for the entire bike in the headlight housing.
 

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Ok, I just took the measurement again. The measurement on battery + to battery - is about 6.1v. The measurement from black wire to the - terminal on the battery is 1.15 volts.
OK this is saying somewhere there is corrosion effecting my connections, or there is something on my bike really dragging down the voltage. Remove the headlight and check all connections inside. The ignition switch should have a couple of plugs on the wires one red one black and make sure those are clean and in good condition. Those wires then go into the headlight bucket and are spread out from there. Again check for corrosion and compare the schematic you posted above to what is plugged into what inside the headlight bucket.
 

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worst case scenerio is you unplug everything inside the headlight bucket and then start plugging everything in one at a time until the voltage peggs. Whatever you plugged in that tanked the voltage is your issue. The biggest power draw your bike should have is the headlight. If the voltage rectifier is bad it can also bring a battery down pretty fast too. Unplug the red/white wire and see what happens. If the bike goes to 6V again you need a new rectifier.
 

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Discussion Starter · #20 ·
Yeesh, this is more involved than I anticipated. Just to be clear: I could have the headlight, horn and brake and spark plugs all working fine, but still have something on the bike really dragging down the voltage?

Part of my hesitation is that a lot of the connections on my bike seem permanent, like I can't disconnect them and reconnect them again. Many others are wrapped in many layers of electrical tape and are hard to access, so I'm just afraid of messing something up and not being able to put it back. Maybe a good winter project would be to rewire this whole thing.
 
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