Need to identify make and model of the truck, since they don't all use the same instrument panels. It sounds like you're referring to a Volvo dash light which comes on when there isn't enough air pressure built up to hold off the spring brakes, although I don't recall it being upside-down.
Lambda sensors. The 3 leg symbol (upside down 'Y') is the greek lambda symbol
mass fire
Mass Fire
It is still a triangle.
rhombus
The upside down purple triangle was actually used to identify Jehovah's Witnessess
An upside-down triangle. It does not matter from which direction you view a triangle, it will still be a triangle.
In mathematics an upside down triangle corresponds to the gradient operator and is sometimes called "del". The Greek symbol of an upside down triangle is called "Nabla".
at the top. The "base" of a triangle is arbitrary.
Upside down triangle bro ;)
upside horseshoe on the car
lalallalalalalallala