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Discussion Starter #1
Hi guys,

New to the forum and hoping it will be very useful.


I have a 1978 XL250 with an electrical issue i cant work out.

My neutral light and horn will only work when the brake light is on.

Also the back light isnt working at all.

I have changed the rear bulb and checked the inline fuse.

What kind of area could the fault be?

cheers
Ben
 

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Has the electrical system been fiddled with / altered from standard at all? My first thought is that there's a break somewhere between battery/ignition switch positive and the point at which the various "consumers" branch off. Does it matter which brakelight switch (front or rear) is on? Without a wiring diagram I'm just guessing, though ;)
 

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Discussion Starter #3
it kind of has been fiddled with but not changed by me. When i got it all was working and the dealer had disconnected the indicators (as they have been removed).

The front brake does not have a brake switch.

I have been messing with the speedo a bit and headlight, which could easily have caused an issue, due to the amount of wires around this area, I guess. To be honest the wiring is a bit of a mess.

I agree i think its a break somewhere, or an earth issue maybe?

With the headlight off the brake and neutral bulbs are a lot brighter too, as expected.
 

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Hi guys,

New to the forum and hoping it will be very useful.


I have a 1978 XL250 with an electrical issue i cant work out.

My neutral light and horn will only work when the brake light is on.

Also the back light isnt working at all.

I have changed the rear bulb and checked the inline fuse.

What kind of area could the fault be?

cheers
Ben
Get the wiring diagram- maybe from a manual and work thro' the colour coded wires headlamp joint areas/ h bar switches / to rear light that you are having issues with.
Also check neutral light wire to Green lamp.

Sent from my SM-G901F using Tapatalk
 

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Discussion Starter #5
yeah someone else said a similar thing. start with the faulty rear light and work towards the connectors and switches.
 

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As far as I know your headlight and tail light run direct from the flywheel. They will not work unless the engine is running.
The stop light and horn run off the battery.
It sounds like when you operate the brake light switch the current is going to earth through the horn and neutral light connections.
I found these wiring diagrams online which are probably good for your model.
R4L: XL350 Wiring Diagram (and XL250)

I would print one or both out and carefully trace each circuit. Print out several copies A3 size if you can.
Check against what you have on the bike and correct it.
Someone has connected something back to front.

Adam.
 

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Discussion Starter #7
Adam your'e a star, thanks for the diagrams.

I was fiddling with the ignition and the neutral light flickered so i've ordered a new one and will see if that changes anything. i've also ordered a new brake light switch to see if thats at fault. cheap enough parts to gamble.
 

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I've got a Haynes manual .. can take a photo of the wiring diagram of you like.... Let me know and will post in the a.m.

Sent from my Hudl HT7S3 using Tapatalk
 
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Discussion Starter #9
Thanks for the offer but I have the manual now. I'll still print them out as it might be easier to see what's what, plus I can leave the prints with the mechanic if I take it there.
 

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Discussion Starter #10
UPDATE.
with new ignition and brake light switch fitted i now have neutral light and horn working as they should.

The problem i'm left with is, if the lights are on the rear light works but both filaments are lighting up, and therefore the brake light isn't "active" . if lights are off the brake light works and again both filaments are lighting up.

so, getting there i guess. hopefully it will just be a case of messing with the brake light system and nothing else.
 

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Check the connections to the rear light...... Should have 3 connections- one to "earth", one to brake light switch, and one to the main light switch. It seems as though the two "feed" connections are joined somewhere, so lighting both filaments whichever source is ON. Could be a duff bulb, but you said, I think, that it's new.

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Discussion Starter #12
yeah bulb is new and it does have 3 wired connected to rear light.

is it better to start at the bulb and work towards the front or vice-versa?
 

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Look at the rear light wiring.
Green and yellow wire puts 6 volts into the brake light filament only when the rear brake light switch is operated.
The Brown wire puts 6 volts into the tail light filament only when the lights are on.
The Green wire goes to earth, in other words it takes the electricity that has been used by the bulb filaments back to the battery negative terminal.

Take the lens off and take the bulb out.
You will see two terminals inside the bulb holder, one will connect to the brake light filament, the other will connect to the tail light filament when the bulb is correctly inserted.
Check to see if the terminals look OK, what I mean is do they look separate or are they somehow mangled together?
In theory it is impossible to put the bulb in the wrong way round because the little "ears" on the bulb sides are at different heights.
You will observe that the bulb holder has grooves in it that terminate at different heights thus ensuring the bulb can only locate one way round.
Does that all look OK in there?

Do you have a multi-meter to test things with?
If so test the individual terminals in the bulb holder, one should get 6v only when brake light switch is operated the other should only get 6v when the lights are on.
If you dont have a multi meter then get one!

As hotbulb says the wring has got "confused" somewhere or maybe the connections inside the bulb housing are damaged some way.

Follow the green/yellow wire back to the brake light switch. It should not be joined to anything else and it should not have any bare wire where the insulation has worn off.
Follow the brown wire back from the tail light, it should disappear into the wiring loom and re-appear at the other end where it goes into a block connector near or inside the headlamp.

Adam.
 

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Discussion Starter #14
once again, thank you very much Adam. i do have a multimeter and a bro=in=law who knows how to use it. I'll follow your guide and see what we can find.
 
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