[TenTec] delta 580 on 10 meters?

[Stuart Rohre]

You can open up  a mike plug and the shielded wire will be the mike audio. 
Or if there are two shielded wires, try putting the meter across them, and 
blow into mike or whistle.  The AC meter should show some millivolts if the 
mike is working.

You need to get the manual for the radio, so you can see if the mike is 
wired wrong for this radio.  Very likely.

GL,
Stuart
K5KVH