How to track down electrical/charging problems?

[hypophthalmus]

Okay, this has nothing to do with Kymco (it's a Yamaha XV250), but I'm stuck and exhausted the relevant forum. In any case, I think most bikes have a pretty similar charging system.

I have two electrical problems, and I'm not sure if they're related:

One problem is that when the turn signals flash, every other light dims. These lights are fed on different positive lines after the ignition switch, but they share a ground.

The other problem is a charging voltage of up to 13.2v, measured at the battery  -- low.

It looks like (according the wiring diagram, and what I can find) all the components are grounded to the frame through a single ground point. That point seems to be good as far as I can tell. No difference cleaning it up, no difference moving it to negative battery post.

Stator resistance measures good -- all about 0.4 ohms between the leads. It's a tiny bit higher than what the manual says, but it's possible that the stator just changed. No continuity to ground. VAC output is also good, 15v idle, 40v light throttle.

I did some kind of test for the rectifier that I found online, measuring with the diode function -- I don't remember the details, but it apparently passed.

The VDC output measured at the rectifier gets is up to 14.0v. Much better. If I measure with one lead at the battery, one at the rectifier (positive/negative doesn't matter), I get 13.8.

My best guess is that there's a bad wire or a short somewhere, but I just don't know. And I don't know how to find it if there is.

[hypophthalmus]

Oh, and the voltage of the battery is 12.5v with everything off. So that's probably fine.

[MJR]

Has the bike always done this or did this problem start recently? Honestly I think this could be normal for a stock electrical system voltage loss but here's a few thoughts.

You can use a volt meter to check for voltage loss across wires or connections if that's what you suspect.  Positive or negative it doesn't matter just connect it from ground point A to B or positive point A to B and see if you read a larger voltage between certain points than others you have found the problem.

As far as the battery goes once the bike has been started it's only purpose is to act as a electrical filter basically stabilizing voltage fluctuations. A fully charged battery should have a certain voltage according to voltage to state of charge charts such as this one. https://www.energymatters.com.au/components/battery-voltage-discharge/ It's possible too that the battery is resisting taking a charge fully too and not performing as it should any more depending on age and life it's had.

Hope this helps.

[hypophthalmus]

I'm not sure if it's always done this. I noticed it when I was checking my work lengthening the wires for the rear turn signals.

When checking the points, does it matter if everything is off or on?

I started doing this a bit testing for a bad connection between the rectifier and the battery. It's a very small circuit that goes battery -> main fuse -> splice -> rectifier -> battery.

Testing at the rectifier I get 14v. At either side of the main fuse, 13.4v. At the battery, 13.2v. Can I conclude then that the length of wire between the fuse and the rectifier is compromised? Or can some kind of problem outside of the circuit cause this? (I have a weak understanding of electricity).

Would it be better to test with everything off and measure the voltage drop as the connections get farther from the battery?

[CROSSBOLT]

Your understanding is just fine, you are WAY ahead of most! Don'T know if I read how old this bike is but you could be having problems with either poor connector continuity and/or poor connectivity between wire (s) rand terminals. PITA to find, easy to fix.

[MJR]

When checking the points, does it matter if everything is off or on?

With power and the load running is the only way to see if point A to B has a higher voltage drop than point B to C.

[hypophthalmus]

Okay, I've educated myself about voltage drop testing.

I decided to to try testing with just the lights on, engine off. Since that's easier to understand than having the rectifier output involved.

Measuring between the negative battery post and the spot where everything apparently grounds, there is virtually no voltage drop (don't remember the exact number).

Measuring from the positive battery post to the fuse, there's already a .2v drop. Measuring to where it feeds into the ignition switch, that's up to .45 volts. And measuring at the two wires that come out of the ignition switch, it's up to .8v and .9v.

If I jump between the positive post and one of the wires that come out of the ignition switch, the headlight just about stops blinking with the turn signal on.

So it sounds like it's the positive line that's the problem. But I can't point to just a single component that's problematic.

[MJR]

Probably sounds about right for stock wiring. If you want better voltage to the headlight then put in a relay triggered by the old headlight wire and run a 14ga wire from the battery to the relay and to the light. Even better add another 14ga ground from the battery to the light.

[hypophthalmus]

Supposedly the blinking isn't normal behavior, so I guess I sided with my gut feelings that the values were high. I'm not too concerned with the headlights blinking per se, although that wire does also supply the ignition system.

I was thinking the .2v drop at the fuse might also explain the weaker voltage at the battery than the rectifier with the engine running... maybe that's normal though and I really should just be thinking weak rectifier/regulator.

Using a relay sounds pretty clever.

Makes we wonder though... is there a way to take the wires out of the connectors and rebuild them? Or I assume the headlight connectors are some kind of standard? But are the others typically some kind of standard?

[CROSSBOLT]

Rebuilding connections/connectors depends. Terminal lugs are crimped onto the wire. Corrosion can sometimes be overridden by soldering. Usually replacing the terminal is preferred. But then you may be faced with some "special" OEM only terminal which then must be carefully pried apart, cleaned and soldered. Connectors are also crimped on the wire(s) so the same thing applies BUT first ya gotta get 'em out of the connector shell! This usually involves some really nicely made special tools (spelled expensive) which will release the actual terminal from the shell. Some are designed to be released by small screwdrivers or picks but few are that way. Kymcos are a mix and I am sure it varies with the tide, phase of the moon and may involve reading tea leaves....

Go after the biggest drops first. The relay idea has merit. Bypassing the harness with new wire and teminals may be necessary. Keep posting. How this turns out may set the standard for repairing older bikes or ones stored outside.

[MJR]

Losses are built in from the factory using smaller size wiring and barely adequate contacts/connections. I think it's just normal having two 21 watt bulbs turn on/off pulling voltage down. Larger wires and better connections will help. The other advantage of a separate headlight upgrade harness is a slightly brighter light via higher voltage to the light (common upgrade with some 4wd vehicles). Most connectors on motorcycles you can remove terminals from connectors with a small pick or upholstery T pin. Like CROSSBOLT said soldering and/or cleaning terminals may help a little.

[de dee]

Losses are built in from the factory using smaller size wiring and barely adequate contacts/connections. I think it's just normal having two 21 watt bulbs turn on/off pulling voltage down. Larger wires and better connections will help. The other advantage of a separate headlight upgrade harness is a slightly brighter light via higher voltage to the light (common upgrade with some 4wd vehicles). Most connectors on motorcycles you can remove terminals from connectors with a small pick or upholstery T pin. Like CROSSBOLT said soldering and/or cleaning terminals may help a little.

  I use a small eye glass screw driver,