(02-05-25, 07:41 PM)robbo Wrote: Whilst out on Wednesday, I was made aware that when indicating, my lights dimmed slightly, matching the cadence of the indicator. Thinking it might be an earthing problem, I connected an independent earth to both the rear lights and indicators, but the fault persisted, even after connecting to the -ve of the battery. It makes no difference if the engine is running or not. Thoughts please.

(03-05-25, 05:59 AM)Gaz66 Wrote:

(02-05-25, 07:41 PM)robbo Wrote: Whilst out on Wednesday, I was made aware that when indicating, my lights dimmed slightly, matching the cadence of the indicator. Thinking it might be an earthing problem, I connected an independent earth to both the rear lights and indicators, but the fault persisted, even after connecting to the -ve of the battery. It makes no difference if the engine is running or not. Thoughts please.

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I'd be thinking an earth prob too Robbo from symptoms you're getting.
Dunno if you're aware or not, but these old Yamaha's have a shabby inadequate earth from factory, main earth lead is Battery ground direct to a starter motor bolt.
I'd be removing both ends of the main earth strap, Ohms test it for resistance with a meter, if it's high bin it & replace it, you can have green death within the crimp on either end of the strap & not see any visible sign of it externally.
While starter bolt is out, run a tap thru bolt thread, blow thread out, avoid using grease within an earth connection, yes paint grease or copper slip over it externally, never grease internally, a bare metal connection always works best, ensure you've clean bare metal on starter body & under bolt head, clean up both sides of earth strap at both ends if strap tests good with a meter, I'd also check the single white connector on the Black ground wire that runs over battery top, clean that up too, seen load of these failing, corroded & loose etc, if it's got green death, cut it out & replace it, if it's loose squeeze it up with pliers.
It's a good move on these old bikes to run a fresh heavy gauge earth wire direct from Battery ground to chassis, do same at both headlamp 3 pin plugs.
If that doesn't fix the fault, you've potentially some issue with a bulb connection or a even an incorrect bulb fitted.
Seen loads of 24v bulbs fitted.
Some modern bulbs have elongated soldered connections & don't work well in older Jap bulb holders, they arc across & can cause poor earth like symptoms.
Have you fitted any bulbs or Led's recently? 
LED's can cause all sorts of problems in older bikes & cars.

If all the above checks out good, I'd be going thru the loom, starting at rear, pull every connector apart, check they're tight & clean, meter probe each side of every connector, wash out any grease you find, no grease conducts electricity.
Main loom multi-plug behind left front flasher is a well known corrosion point.

Be methodical is my advice or you'll just be wasting time chasing your tail.

Have fun ?

(04-05-25, 08:18 AM)Trebus Wrote: Hi Robbo, you can also take a look on Christian’s site for some good info. It’s in German but translates ok in my safari browser on the phone.
http://cvieth.bplaced.net/motorrad_licht.html