Low beam not working.

[Bibio]

if its the sport then there is a small negative terminal block inside the cowling that can fur up. it has a black plastic cover over the top of it with a small clip on the side. remove the cover and inspect the connectors (there is a metal bridge piece, pry off and clean) on the block and apply acf-50.

also the main loom to sub loom connector inside the cowling terminals are notorious for furring up. again apply acf-50

each of the above requires you to remove the whole headlight cowling to gain access to the connectors. on the final removing of the cowling you have to hold the cowling in one hand and undo the main loom to sub loom block at the same time or the cowling wont come off. no need to remove the screen.

when putting the cowling back on remember to connect the main terminal been there done that

[SV650rules]

Sounds like corrosion on the low beam fuse connections, if you get voltage drop down to 9.5v on high beam fuse maybe slight corrosion there as well, or on connector between fuse box and battery.

Bibio- He is quite an expert at taking the headlight off now as he has had it off about 10 times in the 2 weeks of me having the bike lol. He has had a look at the negative terminal block, removed the metal bridge piece, cleaned it up, sprayed with ACF50, reassembled but still no low beam.
SV650rules- The battery is measuring 12.1v and high and low pins on the white connector by the clocks both measure about 11.9v. It is only when connected to the headlight assembly that the voltage on the high beam drops to 9.5v and the low beam voltage drops to 0.05v.
The side lights and high beam are still working fine

He has just measured the voltage at the black three pin connector that pushes onto the bulb and there is about 11.8v at both high beam and low beam terminals. This is while it is NOT connected to the bulb. With the connector pushed onto the bulb high beam works and measures 10.1v at that terminal. Low beam does not work and measures 0.04v.

[Bibio]

have you tried new bulbs?

have you tried the voltage across the battery terminals while the bike is revving at around 5k?

Yes bulbs were the first thing he tried. And yes he has tried revving the bike and testing the voltage he said it was 14v

He has just connected the white wire from the main loom to the headlight assembly and we are getting + 11.8v at 3 other pins in the white connector on the headlight assembly - the brown (side lights positive ), the earth pin and the yellow pin (main beam ).
So it looks like the white wire must be shorting out somewhere in the headlight sub loom ... ?

[SV650rules]

When there is no current being drawn ( no bulb in socket ) the voltage on bulb will be same as battery voltage even if connectors are corroded, it is only when current is drawn ( bulb plugged in) you get voltage drop, and the golden rule of electricity is that the largest volt drop is across the largest value of resistance, now the bulb filament is low resistance compared to a corroded connector so you get half a volt across bulb and 11.5 volts across the bad joint. OP said when he connects bulb common direct to battery negative still no joy, but when he bypasses fuse with a wire direct to battery positive the bulb lights up (even when using original earth path), so problem is not in earth circuit, it must be in live feed via the fuse.

Just tried another lot of bulbs out of his daytonna and still the same problem but he put my bulbs into his bike and they worked fine. Stripped insulation off headlight sub loom and no obvious damage to white wire where it could be shorting against other wires.
Measuring continuity between the white low beam wire, the brown side light wire, the main black and white earth, and the yellow main beam wire. If we unplug the connectors from the bulbs there is no continuity.

Thankyou SV650rules he will check that tomorrow he has had enough now and is off to the pub lol