It all started with an indicators fault on my Honda CM125CC. Stationary with no engine running they worked fine. Engine running at tick-over they worked fine. Riding down the road they didn’t unless I put my foot on the rear break pedal.
Its obvious, I thought, its an earth fault somewhere. So, I proceeded to clean and check every earth wire connection on the bike and after several hours of work made absolutely no difference to the issue.
In that case it must be the flasher relay. So I bought a new one, fitted it and that fixed it ……. not!
Out came my multimeter and I checked every voltage and resistance level mentioned in the Haynes manual. Nothing!
Having spent two weeks off and on working through troubleshooting the problem I could safely say I was no further forward.
My Dad always used to say if you can’t find the answer, you don’t understand the problem. So I put everything back together and did some further basic tests.
Engine off and it worked fine. I started the engine and let it tick-over and it worked fine. I gently increased the engine revs and at around 3000 rpm the indicators stopped working. I dropped the revs a little and they started again. I increased the revs to 3K and they stopped. I put my foot on the break pedal and they started. Foot off the break pedal and they stopped. I turned the headlight on still with 3K dialled in and they started again. Still with me!
All this testing started to give me further clues and I dragged the multimeter out again and measured the voltage across the battery at different rev points and realised that the volts was going off the scale. The issue was the voltage regulator it wasn’t capping the charge voltage and when it got to 15V, the indicators stopped working. Switching on the headlight or anything else electrical would pull the voltage down enough to make it all work.
Bit miffed as its not long since I replaced the regulator. Anyway, bought a replacement and fitted it. It didn’t make a jot of difference. Still too many volts. Threw everything in the garage, slammed the garage door and went to bed.
A few days later I decided I was not going to be beaten by this and ventured back to the garage. Wheeled my trusty steed into the sunshine and got my folding camping chair out. Radio on, bucket of hot tea and I settled for a siege!
I ran various bits of wire out from connectors in the wiring loom so I could check stuff without having to take the bike to bits. This also meant I could check stuff with the engine running. I wasn’t actually sure what I was looking for so the bike looked a bit like a shaggy dog with threads of wire everywhere with bits of coloured tape over the ends so nothing shorted out and I could tell which were supposed to be live and which were supposed to be earth.
I then started measuring volts. Some of it was really basic stuff like volts across the battery. I then started getting a bit more technical as I started to think things through a bit – the tea was working.
I started to investigate more closely the volts at the regulator end of the black wire which is the sensing wire and drives the regulator. I realised this was seeing about a volt less than what I was actually measuring across the battery. My very simple mind was telling me that this could fool the regulator into thinking the battery was not charged when it actually was. I followed the trail of this wire through all the various connectors. I fairly quickly arrived in the headlight and discovered quite a bit of corrosion on the terminals of the big connector in the headlight. I cleaned the connectors thoroughly and then continued to the next block cleaning as I went.
I then reassembled the bike and checked voltages again. Much better. I was now reading exactly the same on the black as at the battery. Convinced I had solved the problem I then reassembled everything correctly and removed all my test leads.
Ignition on and check indicators. They work. Start engine and check indicators. They work. Rev engine to 3K and check indicators. They don’t work. Another cup of tea and a calm pill!
More in desperation I somewhat randomly removed the new flasher unit and put the old one back in. Ignition on and check indicators. They work. Start the engine and check indicators and they work. Dial in 3k and check indicators and they work!? Dial in lots and they still work. Foot on break pedal and they still work. Helmet on and a quick whiz round the block and they still work.
So, what was the problem. I can only apply a half arsed guess but I would say the corrosion in the wiring caused the voltage regulator to go a bit awol. The new flasher unit I put in may have been faulty to start with or could have been damaged by the over voltage from the regulator. Anyways I now have a growing stock of voltage regulators in my parts bin and in future I will check for corrosion in the wiring before I do anything else.
I guess the moral of the story is, on a 30 year old bike always look for corrosion in the electrics first and only when thats been exhausted look for a component fault.