Honda-SOHC
SOHC.co.uk Forums => Project Board => Topic started by: Laverda Dave on September 28, 2025, 06:09:03 PM
-
I am currently racking my brain with the 'unique' TL125s wiring.
There were no handlebar switches with the bike and the loom was unknown, it certainly isn't a TL for sure.
I have got quite far with the rewire but I now have two problems I cannot solve.
First one is the handlebar switches. TL parts are unobtainable so I have used a XL125 for the L/H side and a CL125 for the R/H side. Both switches mimic the originals but that's it. The issue is really with the R/H replacement switch which is basically an ON/Off lighting switch only (main/dip/indicator & horn is in the L/H switch. The R/H switch has four wires coming from it, yellow/white, blue/white (these appear to be connected with a moveable contact inside the switch. These also appear to contact in the OFF position. The other two colours are brown/white & Black. These are also linked with a moveable contact and operate in the ON position.
The problem is the Honda TL wiring diagram shows the correct TL R/H switch has 8 cables coming from it even though it serves the same function as the CL replacement switch I have fitted. The real problem I have is the Yellow/white and Yellow cables from the flywheel alternator are shown to feed into the TL R/H switch as two of the eight cables. The CL switch only has the Yellow/white cable so I therefore don't know how to wire the remaining Yellow cable from the alternator into the CK switch! Does anyone have any ideas of how I can wire the 'spare' yellow cable because it's obviously needed to supply power to the lights somehow?
The second issue concerns the Silicone diode rectifier. The TL wiring diagram shows it to be wired into the battery after the main fuse (but other diagrams show it to be wired in parallel with the battery so that's confusing as well!) on one leg (the positive side of the diode) with the negative leg going again to the R/H handlebar switch (and the CL switch doesn't have this cable either! Looking at the wiring diagram the yellow cable from the alternator appears to connect with the diode cable when the headlight is switched on.
Electrics really aren't my forte, any ideas welcome!
-
It's going tricky this one. Try having a look at the wiring diagram for the Honda MT125 (2-stroke)...similar set up to the XL125s but the diode is fitted very close to the battery.
-
What you have is a charging circuit rather like old Triumphs, i assume the TL is 6 volt,
What happens is that when you turn the lights on it connects extra coils in the generator to provide power for lights, if these were permanently switched in you would boil the battery.
If you cannot find a correct switch(450 twins had a similar switch) what you could do is fit a "clipper" diode and wire the generator for pemanent full power. The clipper shunts excess voltage to earth like the 650 British bike Zener but at 6 volt not 12
-
Thank you both for your replies.
I very nearly joined the two alternator wires together (yellow/white & yellow) after watching some YouTube videos (dangerous!), I'm glad I didn't now as Bryan states, I might well boil a brand new mottabatt🙁.
Thanks for the info about the MT125 wiring Al, having looked at it closely I think you've pointed me to the answer, put the yellow cable through the silicon diode rectifier. This will save using the clipper diode I hope.
I'll report back tomorrow once I get into the garage and removed the splinters from my fingers after scratching my head all day!
Cheers
Dave
-
This sort of genny does cause head scratching, i will try and simplify it a bit.
Usually 6 seperate coils wired as 3 pairs each pair joind in series so 2 wires out.
1 pair always connected to rectifier giving enough to run ignition.
The others not connected so nothing comming out.
When you turn lights on the switch also connects the extra coils to the system giving a bigger output to run lights.
This is the old Lucas idea, i think the Honda may only have 2 coils in there, 1 for low power then the 2 together for full power, it does make for a complicated switch!
-
Thank you both for your replies.
I very nearly joined the two alternator wires together (yellow/white & yellow) after watching some YouTube videos (dangerous!), I'm glad I didn't now as Bryan states, I might well boil a brand new mottabatt🙁.
Thanks for the info about the MT125 wiring Al, having looked at it closely I think you've pointed me to the answer, put the yellow cable through the silicon diode rectifier. This will save using the clipper diode I hope.
I'll report back tomorrow once I get into the garage and removed the splinters from my fingers after scratching my head all day!
Cheers
Dave
Thinking about this again overnight and your response this morning Bryan (yes, it is the two coil type alternator as you describe). My only concern is if I connect the spare yellow cable through the silicon diode rectifier and thus into the battery will this method then potentially boil the battery because the power has to go somewhere? I can't ground it to earth because the bike has lights and indicators erc.
I might be over complicating things, I'll report back once I get a chance to look at what I have later.
I should have paid more attention in physics at school!
-
There is normally 2 generator windings...1 rectified & 1 not.
The XL250s/500s uses a combined rec/reg for charging/clock lighting/indicators/ect
I have lifted the schematic from the XL500 shop manual, hope that you can see it
-
If its like the 500 its different from what i described, one coil charges the battery and works ignition then lights are on ac power
-
Dave if you have a scematic for both switches you can send me i will try and work out a way of using the switch you have to operate wires using relays for you, my email is in my profile but you should have it anyway
-
Thanks both, heading out to the cave now and will report back.
Cheers
Dave
-
Hi Bryan.
I've sent you a mail to your email address, can you let me know if you've received it please as I got a bounce back in my inbox it couldn't be sent yet it appears as sent in the outbox!
-
Nothing yet mate, did you use the .org.uk address?
-
Hi Bryan.
I resent it this morning to the .org address. No undeliverable mail message sent back so hopefully it's up in the clouds on its way to you👍.
-
So the wiring is all now in thanks to Bryan and his skills with wiring and understanding relays.
I started the bike (it started second kick after I don't many how many years of standing).
I have a few problems though, the number one being the headlight, horn and dash lights don't work just off the battery despite the black (feed wires) being live. The rear light though does work when powered just from the battery as do the indicators.
The neutral indicator light only works when the the lights are switched on (although the lights themselves do not work, only the neutral light).
Not being used to 6v generator systems with a separate coil for lighting am I correct in assuming the headlight, dash lights, horn and front stop switch will only work if the engine is running although this seems contradictory considering the feed wires are live?
I've run a separate earth to the battery from the frame earth points just to be 100% sure I have a good earth.
Very frustrating to put it mildly!
-
Lights would only work with engine, indicators, horn, both brake light switches and neutral should work from battery, i will have another look at the diagrams for you
-
Thanks Bryan. The rear light works on the battery when using the light switch. Indicators work on the battery.
It's not bade easy with the MT125 R/H switch, XL125s L/H switch and a main loom (ot the 3rd I've kept) from an unknown bike. I've been pouring over the wiring diagrams of all three bikes and can't understand why if the black feed cables are live why isn't anything else working. Just taking the horn off now to test it.
-
Tested the horn on a battery, it works so a wiring fault somewhere.
I solved the brake light problem as well. The brand new front brake brake light switch was faulty, it's permanently on. I swapped it out for a spare one I had for a 400/4 and it now works. So the brake light works (front and back) with the ignition on as it should.
The neutral switch is puzzling, sometimes it will work when the main light switch is operated (but doesn't work when only the ignition is switched on) and sometimes it doesn't.
All frame earths are good.
The relay is definitely working, I can hear it energising when the R/H main light switch is used.
-
Dave, i have replied to your email, just in case its hiding again mate!
-
Hi Bryan, yes thank you for your reply, I'll be out in the garage later this afternoon with a mug of splosh and some renewed enthusiasm 🙂👍.
-
OK Dave, while you are there, only reason for neutral light not working when plugged into black is a bad connection or brokenish wire, check the state of the bulb holder as they corrode and the centre contact goes bad
-
Thanks for your help Bryan.
I checked the continuity right through the cable (green / red) and it was spot on. The switch itself was ok and I was getting 6.3v on the feed. I was scratching my head for ages. I worked yesterday morning but then didn't. I eventually ran a cable from an engine bolt straight to the battery earth and it worked! Really odd considering I checked the frame earths and they were fine. I've now run an earth cable from the top engine bolt to the main battery earth cable.
I'm going to start the bike tomorrow and check the lighting is working with the engine running. That's the last thing to check now, everything else (apart from the horn that I'm pretty sure is defunct because I have 6.3v feed and the earth is good after testing.
I'll let you know how I get on and report back.
Thanks for all your help with this.
Cheers
Dave
-
No problem Dave, if you painted the engine brackets that would give the earth problem, from the factory the brackets had no paint where they touched the engine and where cable touched