[Paul Workman]

If stepping on the brake causes change in the luminance, "grounding" is the first thing that comes to mind. The FSM should help. But, in the mean time, the two circuit ground reference points are on the back of the block at the edge of the bell housing, each right/left bolt is about 6 inches either side of top-center of the periphery. There are 4 lugs on one bolt, and 5 lugs on the other.

As for the connectors on the instrument cluster, there are two; the main one at the corner of the board, and the other is at the top, which serves the LCD pannel. Both connectors can be and should be replaced, if there is any sign of "frosting" (whiteish oxidation) on the pins. (I ran across those connectors a few times when I was searching for parts for the board. I'll see if I can dig them up again.)

P.