KITT car ASCII art

JavaScript (ES6), 65 67 bytes

EDIT - Fixed for negative values. Now supporting N >= -8,000,000,000, which should provide a fairly good extended operating time in AUTO CRUISE mode. :-)

let f =

n=>[..."------#++-----".substr((n+=8e9)%7,8)].sort(_=>n/7&1).join``

// testing 28 frames
for(var i = -14; i < 14; i++) {
  console.log(f(i));
}

Animated version

let f =

n=>[..."------#++-----".substr((n+=8e9)%7,8)].sort(_=>n/7&1).join``

let n = 0;

setInterval(function() { document.getElementById("o").innerHTML = f(n++) }, 90);

<pre id="o"></pre>

JavaScript (ES6), 90 87 bytes

n=>"01234567".replace(/./g,i=>"-+##"[g=n=>!((+i+n)%14&&(n-i)%14),g(n)*2|g(n-1)|g(n-2)])

"-+##" is indexed by a bitmask, where bit 1 signifies an active light and bit 0 signifies a dimmed light. Active/dimmedness is now calculated by adding and subtracting the current position from the desired position and seeing if either result is divisible by 14.

Jelly, 28 22 bytes

-6 bytes thanks to the help of @Dennis! (upend first, then concatenate)

”-ẋ6;“#++”ṙ7Ḷ’¤Ḋ€U;$⁸ị

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Or perform four oscillations with a bonus easter egg!!

How?

”-ẋ6;“#++”ṙ7Ḷ’¤Ḋ€U;$⁸ị - Main link: n
”-   “#++”             - strings "-" and "#++"
  ẋ6                   - repeat six times: "------"
    ;                  - concatenate: "------#++"
              ¤        - nilad followed by atoms as a nilad (ie make a constant)
           7Ḷ’         -     range(7) decremented: [-1,0,1,2,3,4,5]
          ṙ            - rotate left by (makes)-----------> ["+------#+",
               Ḋ€      - Dequeue each                        "------#++",
                   $   - last two atoms as a monad           "-----#++-",
                 U     -     reverse (vectorises)            "----#++--",
                  ;    -     concatenate                     "---#++---",
                    ⁸  - left argument (n)                   "--#++----",
                     ị - index into (1 based and modular)    "-#++-----"])