Volvo Repair: Broken speedo on 240 gl, volvo 240 gl, volvo dealership

Question
I have a 1987 Volvo 240 GL and the speedometer is broken. I called a Volvo dealership and they said that there are many sensors that that could cause the problem. So im basically asking what's wrong and how would I deal with it?

I was under the car a couple of days ago and saw a cable attached to the transmission badly beat up could that be the problem?

Thank you

Answer
Zach, that guy was smoking crack.  No, that cable is for the Overdrive solonoid.  The wires you want to look at is the ones on differential sensor.  Most likely the problem is in the speedo head.  I perform customizations on stock clusters.  If you are interested, I can send you pictures of my work.  Send me your Email and I will be glad to send you some samples.  Roger