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Old 09-15-2008, 10:10 PM
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Tach needle

I am almost finishing a 4 year renovation on my 1984 Chevy C-10, I have adapted a tach from a 1980 Chevy truck, which I bought in ebay and this work fine, except that when the switch is turned off the needle comes up to where 2000 rpm is shown. As soon as the switch is turned to acc needle comes down to 0 and right after engine fire it gives the rpm.
Connection on the tach shows for ground, 12 volts and the coil. When I installed the wire for 12 volts I connected it to acc in the fuse box. Any body knows if this wire must be connected to a all time "hot" 12 volts?
Thanks for your replies,
Luis
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Old 09-16-2008, 06:24 AM
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I have a tach that does the same, it is ok, mine stops at the idle mark when engine is shut down, as to the 2k indication . That just maybe the way it works, some drivers will give the gas a quick rev just before shut down, and if you do this as a habit, that could explain the 2k reading. If you had the thing wired ..... now think about this, as hot all the time. I would bet the battery would be dying on you ..... make any sense here ?
I would move the acc connection of the tach to the (I) side of the ignition, so that power is at the tach anytime the key is on, The tach is not an accessory it is an engine monitoring instrument , as with oil pressure, the radio is an acc.
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Old 09-16-2008, 01:55 PM
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I've seen some of the older GM factory tachs that the needle doesn't return to Zero when you shut the engine off.
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Old 09-17-2008, 01:50 PM
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My Dolphin electronic tach does the same thing, that is sticks at the rpm reading last indicated when the key was turned off. Not really a problem. You can install a time delay relay to the instrument power circuit, or just simply turn the key on again briefly after you turn the engine off to get the tach to settle to zero.
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Old 09-17-2008, 08:51 PM
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Guys, thanks a lot for your replies. I thought I had a problem but you guys helped me with your comments.
Luis
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