if i were to install the unit with out splicing into the dash cluster and rear tail lights what would be the outcome

Suggestion: Please be more clear when asking questions so as to get the answer you're seeking the first time around. We're not all about critical thinking when it comes to translating questions which had little thought put into them.

That being said; I think you're asking what would happen if you didn't splice in the VSS or Reverse wire. Nothing would happen; you would loose a bit of accuracy and have no chance to use a backup camera, but the unit would still be functional.