Am I right in thinking that electrical items that can be used in vehicles via the cigarette lighter socket such as phone chargers and sat. nav. systems etc. run on 12 volt systems and that trucks tend to be 24V. If that is right how can they be used? I assume if you plug a 12V item into a 24V system it will fry. Sorry if its a stupid question! 
Just buy a 24v to 12v dropper, then plug your 12v stuff into that - problem solved 
mike the cig lighter socket will be 24volt but there should also be a 12 volt socket in the truck comonly known as a hella socket to if your 12volt goodies have big plugs you need an adapter with a hella plug but it has big sockets try somelike cdc www.lorrybits.com for ya stuff and yes 24volts will fry 12volt equipment
Most phone chargers will work fine on 12 and 24V, as will Navman Satnav’s.
You know if something is wrong if you can smell like something is burning…
tom tom go 12/24
Pukka Nokia phone chargers are 12/24v. Cheaper phone chargers for Nokia are usualy 12v only (which is why they’re cheaper 
).