LOL I thought you had run over the mechanic too when I saw the title! Anyways your tachometer has the same symptoms mine had a short while ago. There is a little garbage-can looking thing behind the driver side headlight, unscrew that and cut the cord so you can take it off and hold it in your hand. Use a small screwdriver to pry out the inside part. There is a ton of ugly looking silicone stuck on the inside, don't worry about that just yet. Resolder all of the little pins to the wires, as the solder gets brittle and develops cracks over the years. Return it back in your car - if you don't put the little black inside holder back in it, make sure you put something over the silicone as it will grip the outer housing (screw-on part) and rip the pins or wires out again (ask me how I know). My tach works fine now, no more jumping or pegging out.

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TC
Current stable:
- 2004 Mazda RALLYWANKEL
- 2007 Saturn sky redline
- 2004 Explorer...under surgery.

Past: 135i, GTI, 300E, 300SD, 300SD, Stealth