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03-04-2004, 09:11 PM
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#1 |
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Registered User
Join Date: Mar 2004
Location: Long Beach, CA
Posts: 13
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Factory Tachometer
Hi all, my 1976 C/20 454 3-speed manual + granny gear has full factory gauges and the tach. The tach indicates properly about 30% of the time. When it does not indicate properly, the needle runs counter-clockwise. No rhyme or reason WHEN or WHY, BUT, if you are running on the left side fuel tank and QUICKLY bump the switch to the RIGHT tank, the tach will momentarily read properly and then go back to the incorrect reading. Any ideas? I have checked the wiring to the tach from the dist lead and 'looked' at the tack when i had the gauges out to clean the lenses and nothing looks amiss......
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K Wilson 76 Chevrolet Silverado C/20 454 manual 77 Firebrid Esprit 350 auto 78 Lincoln Mark V Emilio Pucci 400 |
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03-05-2004, 12:34 AM
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#2 |
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Oh,you can't buy that new
 
Join Date: Apr 2000
Location: Pennsville,N.J. 08070, USA
Posts: 2,039
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It sounds to me like the tank switch and the tach have a common wire, It can only be the 12V power feed. The other two tach wire are Tach feed from distributor and a ground. it is common for the switch to go bad so there is a chance that when you change tanks it momentarily grounds out . Could also be backfeeding through the common chassis ground too but that would most likely mke several gauges go whacko. DAVE
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"been there, done that, ruined the T-shirt". 2007 LBZ GMC Sierra, ECSB 2006 LM7 RCSB Silverado 98 Vortec project. 94,3500,6.5L 4L80 81 SWB GMC POS finally gone  73 Pinto, stock, w/CragarSS's-eww  LOTS of Cummins trucks. |
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