Major Electrical Prob!

[GreenPony]

Ok, i am about tired of my car doing this. ever since i bought the car when i turn the headlights on either my dash lights go out or get really dim, sometimes they go out and my 2 blinker lights come on. But others it works just fine, i have narrowed it down to a bundle of wires that come in through a firewallfrom under the hood on drivers side..But not sure where or which one 's it is specifically to try and fix. I am so confused on this and just tired of it..And ideas besides something shorting out.Another thing is my tach is stuck when i turn the car on at about 4500 rpms, when i go over that it begins to move , but stays there when i am under 4500, but whats weird is when the car is turned off it drops down to a no idle position.,.,.,PLEASE HELP