Please could anyone tell me what a switch is for on the dashboard of a 2001 FL6 220
Tipper / crane lorry
It shows four wheels looking from above , between two wheels where the diff would be a black square box with a arrow going forwards.
(I have not been able to source a handbook yet)
Diff lock ?
no i have found the diff lock switch which works fine
I have a PTO switch but have a feeling it is something to do with the pto
Is it a clutch dependent/independent PTO? Could be a switch that allows you to run the PTO whilst on the move? Just a wild guess though 
Cross-axle diff lock?
Mid axle diff switch lock,that crosses the axle traction lock when engaged in an Abs moment of doughnut spin. I find it very usefull.
Hi Boris 1971
Not sure if you are jokin but being as the lorry only has a front and a rear axle not sure what benefit this would be and why you would want to use it.
Engaging the diff lock would lock the two drive wheels so I don’t see what more you could do to benefit drive
Perhaps it is fitted, but not in use…?
it defiantly does something and is working but I cant fathem out what
Does it turn the tacho off !! Some naughty previous owner may have used any old switch ,it’s how most get caught out ,like a f12 with 2 exhaust brake warm up switches .
Does it turn the truck into bus for the bus lanes??
lucemm:
it defiantly does something and is working but I cant fathem out what
I have to ask
What makes you say / think that ?
Can you hear something engaging ?
From what you describe it does sound like a diff lock switch, assuming yours is a 4 x 2 ■■
after ticking over for about 10 seconds the engine gets a load on it
if you rev the engine over say 1000 rpm or press this switch which lights up
it removes whatever was loading it possibly by air
sometimes when the switch is on the engine will load again and the light will go out and you have to reset the switch again
PTO
no pto has a separate switch which is air operated that i engage to use crane and tipper
Sorry I misunderstood, I thought the switch increased the revs. I’ve seen the switch, possibly in a Volvo handbook, like you I have no idea what it does though 
lucemm:
after ticking over for about 10 seconds the engine gets a load on it
if you rev the engine over say 1000 rpm or press this switch which lights up
it removes whatever was loading it possibly by air
sometimes when the switch is on the engine will load again and the light will go out and you have to reset the switch again
Sounds like a cold start load thing
I remember the F717 had a cold start device load thing
possibly some sort of warm up device not convinced though
This mysterious loading only happens with the handbrake on. so to unload it you can do three things
switch the switch on or rev the engine above 800rpm or let the handbrake off
so any ideas anyone■■?