what does that light mean the little red light when it turns on, and what should i do about the service light? i got a 1993 850

 

Which red light are you talking about?
To reset the service light follow the instructions on the site I am linking you to.
http://www.troublecodes.net/Volvo/
Once you understand how the system works then push in either 4-1-5-1 Or 5-1-4-1 I frget which one it is.
I can't ever remember which one it is.

 

the little red light is right next to the clock desplay, it hasn't been on for a while. but it use to come on and shut off after driving for a while. hasn't been on for a while now.

 

As per the book... if it's the red light that I think you are referring to;

Ambient Temperature Sensor

The sensor indicates the temperature slightly above the road surface. A red warning lamp lights up when the temperature is in the range of 23F-36F (-5C-+2C). Please note that this lamp does not indicate a fault with your car. At low speeds, or when the car is not moving, the temperature readings may be slightly higher than the actual ambient temperature due to the heat generated by the engine.

Now this is the explanation in the book. I think that it is to tell you possibly when you should activate the winter or traction control because the surface of the ground could potentially be getting icy? I'm not sure, but that's my guess.

 

I have always wondered why that light comes on at 36 and off at 23? My guess is that at 36 it's warning you that it's cold and there could be ice. At 23 it figures you ought to be smart enough to know it's cold.

 

The light goes on at +2 (35ish?) and off at -8 (I think)16ish the reason for this is to let you know the optimal icey road times.
Cheers
Wes