Billybolt,
The electric gauge uses a sending unit that is in the block and is wired to the gauge..the mechanical gauge has a capillary tube which is filled and sealed and goes to a probe that is in the block.
The tube on the mechanical unit isn't serviceable...if it is broken or NFG, it's time for a new gauge. The difference is obvious between these two types. The capillary tube is, as you described, a little tube, not a wire.
The old AD rigs used a small copper tube, you indicated yours was a black plastic looking tube...again, obviously not a "wire".
If yours is mechanical, where the tube goes into the back of the gauge, there will be NO connection...it will end in a weird looking crimp, and won't be detachable.
Both styles are accurate. Some old timers feel the mechanical type is more accurate. I think they are more expensive, and not as popular today.
Hope this helps!
Stuart
