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Just purchased a 1980 L48. While bringing it home the speedo and tach quit at the same time. New Transducer and cable fixed the speedo but can't figure out the tach. Any suggestions where to start?
wayne80
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The tach is a computer board and gauge. It has a feed from the distributor that goes through a tach filter under the hood, then to the dash unit. There it connects to a printed circuit, and to the tach board, which the tach mounts to. There also needs to be a 12 volt lead and ground to the tach board/tach.
Start by checking fuses, and the connections under the hood. Then you get into the dash and look for loose connections. You can use a dwell meter with the black lead connected to any good ground, and then hook the red lead to various points and you can see where you have the tach signal, and where you lose it.
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Check that the tach wire gets to the distributor and isn't damaged. Then bypass the tach filter to see if that helps.
Then, most likely, change the tach board. I've replace two of them in the last three years, including the one on my 25 mile Pace Car. Was told by the guy over on CF who repairs them that the electronics just get old and malfunction.
Easy fix for the later C3s, maybe 30 minutes. Get at it from the front of the instrument panel, removing the clear lense and the gauge bezel. Three screws remove the tach. Change the board and put it back together. Might have to reset the needle by pulling it of and setting it to zero.
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Thanks to both of you. We'll be on it today.
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V
Former Member
Send PMMounds View, MN - USA
Joined: 5/24/2007
Posts: 1034
Vette(s): 70 LT1 coupe, 69 350 HP coupe, 69 390HP 427 coupe, 71 LS5 convert, 85 coupe, 93 coupe
Since they both quit at the same time, I would concentrate on all the areas in common, like power feed, and grounding. It would be quite a coincidence if they both had a different problem at the same time.
Larry
Larry
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in Forum: C3 Electrical, Body and Interior
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