1985 chevy Blazer Speedometer

I just bought 1985 Cheverlot Blazer 2.8 4x4 auto matic trans and the speedometer is not working can you please let me know what and where i should look for the trouble thankyou in advance

[dirty dan]

Check your speedo cable (screws into left side of transmission) to make sure it's not broken. This is usually the cause. You should be able to turn the cable quickly by hand and make the speedometer needle jump.