Hitting highs and lows today. Really up when I found a small VDO tach for my '91 automatic 245 at a salvage yard. Tach has three terminals on the back (+, -, and Gnd), plus the light. Installed tach per some of the groups previous instructions with the white and red signal wire going to + and a ground installed to -. Even wired the light. Upon first engine start the tach went to about 2,000, then jumped to 4,000, then swung hard right and pegged solid against the stop. Now all it does on engine start is immediately peg on the high side and stays there like glue. At least the light works. Have tried different position of ground wire to third tach terminal marked "Gnd", tach doesn't move with ground at this position. Suspect tach is bad, would appreciate any ideas before I look for another tach in case I have accidentally fried this one with my wiring.

Thanks!

Mike