Bike not holding steady idle and stalling when headlight is switched on

[Toado]

Hi all, I have been having an issue with my bike not holding a steady idle for a while now - it's idle when warm (no choke) tends to slip down to about 500 rpm and fluctuate up and down a bit before sometimes trailing off and stalling. It restarts with no issue but can then stall again if I don't feather the throttle to hold the revs up enough. I had thought it might be the pilot jets and have been running an additive in the fuel to see if this helps but the problem has continued (although it seems to be stalling less often now). I took the bike out today to see how it was running (it was a fabulous day for a ride) and I noticed that it doesn't stall and holds a steady idle if I turn off the headlight, which is normally on at all times. This seems to indicate that the issue is electrical, rather than fuel related but what should I be looking at first in the search for the cause? All help will be really appreciated! 

[herennow]

What voltage is your battery at, when last did you charge it?

[Toado]

I'll have to check the battery's voltage but it's only about a year old and it starts fine every time so there doesn't appear to be any issues in that regard.

[Toado]

Voltage checked with the multimeter - 12.81 so that seems to indicate that the battery is fine and it's also getting recharged correctly. Given this, any ideas about what could be causing the revs to fluctuate downwards and then drop to the point of stalling the bike when the idles with the lights on?   

[moe_tunes]

I would check the earth connections at the battery, frame and engine. The one at the bottom rear of the engine is fun to get to....
How are you turning the headlight off? That might give a clue.

[Toado]

thank you, Moe. I'm turning off the lights by using the switch on the rhs near the grip so I'm not doing anything tricky. I'll run a spanner over the earths and see if it helps. I did wonder if it could be a short somewhere or a possibly a faulty rec/reg - are these possible alternative causes?

[Armandorf]

I would inspect cables behind the headlight, also check Handlebar switch wiring loom, it can get caught between the frame and the forks pinching it.

[WonkyMechanic]

Could it be a loose or improperly seated fuse causing irregular voltage to the coils?
 

[Armandorf]

Check every wire and connector from battery and ignition. Disassembly, Clean and reconnect.
Every loose connection can cause this, also temperature Will make it contract or dilate connection gaps