If the speedometer is not working it probably needs a new speedometer cable. If the speedometer is actually broken either take it to as speedometer repair shop or replace it.
Remove cable from speedometer head and squirt proper lubricant through cable housing
call maaco
There are to sizes 110"and 125".
If you look under the truck, near the left rear side of the transmission, check for a cable secured to the transmission by a bolt and clip. This is the speedometer cable, which is probably broken in your case, if it is a 4x4 truck, the cable is on the left rear of the transfer case. You can buy just a cable from your parts store, pull the cable from the housing, it should have a square end about 1-2 inches long on each end of the cable. The cable is secured to the back of the speedometer by a spring clip. If you pull out a cable that is not suare on both ends, it is broken!!
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4.1 liter V6
under dash, far left
Cable Software was created in 1983.
Depending on what you mean by "repair", the common issue for a speedo not working in an 80s Monte, is due to a bad cable, which would just need replacing. Your question needs a little more detail.
Optical Cable Corporation was created in 1983.
Spotlight - cable TV - ended in 1983.