HONDA CG125 - Diagnosis for no running lights?

[wulfprints15]

Hi all,

Almost got my CG all back together. Have fixed the ignition and indicator faults I was having when I last posted here.

I've learnt a bit about wiring doing this but I've come up against a problem I just can't figure out.

I've lost headlight, tail light, side light. I understand the power for these comes from a dedicated AC circuit coming straight from the reg/rec. I've tested the battery voltage when running and it rises and falls with revs showing that this works.

So it charges the battery just fine but I've got no running lights.

Does anybody have any clue on a good route to diagnose and eventually fix this issue? I've looked in my Haynes manual but it doesn't seem to have much info on the matter.

I'm running tests with the headlight and side light out of their housings. Will this cause an issue with earthing? I would've thought not because they've got earth wires going to the bike but thought to check.

PS. It's a 1995 BR-S/T

[stinkwheel]

Are all the bulbs blown? They can have cascade bulb failures.

Check the ballast resistor is intact and making contact with earth (not sure where it is, on the end of the pink wire).

As I recall, they have a split charging coil so if the battery is charging, the stator coil is probably ok. That leaves you with a wiring/switch problem. Do you have a multimeter?

The tail light and the headlight are on two different circuits from the switch and use different frame earths so if they are all gone, I'd suggest it probably isn't the wiring beyond the switch, it's likely either the switch itself or the wiring between the generator and the switch.

Specifically the yellow wire.

First double check you are getting an output. Find the yellow wire coming up from the generrator (left side of engine), measure AC volts between the yellow and earth with the engine running. You'll probably get a wildly fluctuating AC voltage. If no output, you may have an issue witht he coil or its wiring.

Now find where it attaches to the headlamp switch. Should have the same reading there. If not, the wire's broken/detached somewhere en-route.

Now check the brown wire from the switch with the switch on. Again, should be the same reading. If there's nothing there, it's the switch. If there is, the light should be coming on.

EDIT: For others, decent wiring diagram here: https://i.pinimg.com/originals/72/fe/53/72fe537b391e99e7ebb15e3ef83c071b.jpg
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[wulfprints15]

[stinkwheel]

That does seem like a short somewhere.

Take the bulbs out and check for continuity (resistance) between the blue, white and brown wires coming out of the switch and earth, they should all be an open circuit with the bulb out. If there is low resistance, that's the wire you need to check.

Bulb holders for instrument back lights can short out to the backing plate if they are connected up the wrong way round (so the outside of the holder is live).
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[wulfprints15]

[stinkwheel]

I wonder if you misunderstood. I was suggesting you set your meter to measure resistance in ohms. When there is an open circuit, it will read very high and when there is a short circuit it will read very low (as if you touched the probes together).

If the bulbs are removed, engine is off and the switch is off, measuring resistance between the brown, white and blue wires at the first connector after the switch and earth (any bare metal on the frame and engine) should be open circuits. If you get a low resistance, there is a short in that wire.
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[stinkwheel]

[wulfprints15]

[stinkwheel]

[Easy-X]

[wulfprints15]

[wulfprints15]

[stinkwheel]

[wulfprints15]

Okay, I've managed to make a bit of a breakthrough after much irritation today.

Discovered that the yellow wire coming from regulator is connected to the brown wire terminal coming from light switch and going to pilot/tail/speedo even when the yellow wire is disconnected from the light switch.

Turns out the wire coming from the tail light is grounding somewhere on the frame. This explains a lot. I'll take the tank off and figure out where it's doing this and hopefully it'll be relatively easy to fix.

With the tail light unplugged every other light functions perfectly as it should.

[wulfprints15]

[stinkwheel]

[wulfprints15]

All fixed and back together! Thanks very much stinkwheel for your help.

I'm still waiting on a new seat (brown and without a hump which makes it too small for me) but other than that it's all finished.

Here are some photos as promised.

[wulfprints15]

https://imgur.com/a/Jq7QLxm

[wulfprints15]

I don't know if attaching images is working or not so here's the link

https://imgur.com/a/Jq7QLxm