Simplified and confining this to audio taper pots: As you may or may not know, a pot is a variable resistor. By turning 'down' the pot, you are increasing the resistance in the circuit by way of a cermet (a glorified carbon) path inside the pot. As the cermet gets thicker and/or wider, so does the resistance to the point that the current flow for all audible intents and purposes is blocked. So, as the cermet path of the pot can be constructed to ramp up resistance as one dials in counter- (or anti-) clockwise, it can also be constructed in reverse fashion for lefties where obviously, turning the pot clockwise will ramp up the resistance. As you can see, it is not just a matter of merely reversing lead and ground wires. With a volume pot, the volume is bled to ground and simply dies. With a tone pot, a capacitor is added to it so the volume doesn't die but instead, selected upper frequencies bleed off and die. Again, this is a bit simplified but you get the idea.

_________________
You dig?

Thank you Martian,

I forgot that we talk about audio ( logarytmique , in french ) potentiometres not linear.

The lefty or righty is for Audio pot . Linear pot are the same for left and right use.

But we don't use linear pot in guitars

Thank's and sorry for wrinting wrong information

You're quite welcome.

Believe it or not, some manufacturers do indeed use linear pots in their guitars but logarithmic is essentially the industry standard.

Again, glad to be of assistance and there's nothing to apologize for; live and learn!

_________________
You dig?

is there a difference that can affect the sound using a bad right pot wired to fit a left handed pickguard?

Any "bad" pot can and usually will affect the sound.

_________________
You dig?

Ops I meant "bad" for a right pot wired to be placed on a lefty pickguard.
Thanx

No, provided it is wired correctly and you can deal with the directional confusion among the other pots.

_________________
You dig?

Then, are different on the external view a left and right pots?
I bought one lefty but I cannot recognize it from a right one

so if I put a right pot I have to turn it on the opposite way than my actual ones installed?
I don't want to have 2 kind of direction to remember at...

Yes. Frankly, I didn't think you would.

_________________
You dig?

Thank you.
At this point I hope I have a real left handed volume pot.
Because if I take the guitar to my tech and he gives me it back with the pot that works on the opposite way as the two tones... I don't know

to avoid problems I'll tell him: this is or should be a dedicated left handed pot, so please wire it as a left handed pot.

You're welcome.

Tell your tech to meter it in order to confirm that it is a left handed pot BEFORE he begins wiring it.

_________________
You dig?

Thanx so so much
I'll keep you all updated
at the moment I still have to get the pickups. A new volume pot ( lefty ) and a new switch are already at home.

then he just have to note how's wired now and do the same later...

Yes, provided that your guitar is in fact, wired with left-handed pots now.

_________________
You dig?