The other definition is false. On the dash does refer to the dashboard of a car, specifically the gauge panel. The number refers to the highest speed on the speedometer.
The Boss - Rick Ross
I've got a Chevy with a 454 in the hood and it's got 125 on the dash.
(Most classic muscle cars displayed a top speed of 125 on the speedometer.)
T.I. - Big Things Poppin'
Think I won’t pull up in something with 200 on the dash.
(High-end supercars, particularly of Italian origin, commonly have the top speed of 200 on the speedometer.)
An answer to the rhetorical "how's it going?". Usually given when someone at work asks how you are and it is quite obvious that you have a crappy job and are just as broke as the next person. Most often used by cab drivers when business is slow.
Dean: Hey Greg, how's it going?
Greg: Living the dream, brother, living the dream.
taxi Greg how are you job life
Originates from hunting dogs, commonly a greyhound not knowing what to do until it sees it's prey "the rabbit". Ie it's clueless and doesn't know what to do or where to go until it spots the rabbit then it takes off with a purpose.
If you need to do something and people are in your way you say "let the dog see the rabbit". Ie. let me see what I'm meant to be doing.
This is a situation when someone tries to futilly reform the way things are done in a failing system.
The consolidation of domestic agency intelligence under the banner of "Homeland Security" is nothing more than Rearranging the Deck Chairs on the Titanic.