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1969 AMX Tach - Driving me crazy |
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musictoyz 
AMC Nut 
Joined: Apr/17/2012 Location: cumberland, me Status: Offline Points: 377 |
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 Topic: 1969 AMX Tach - Driving me crazyPosted: Jun/17/2018 at 8:33pm |
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1969 AMC AMX 390 Tach - Auto - All Stock Tach turns on mmm every 5th or 6th trip I pulled the dash off, ran a new wiring harness around the window to test. Before I pulled all the wires out of the bay....no tach the car runs....if I disconnect the old wires or the new wires...engine dies. either set of wires...no tach... Butttttt the tach does work ? just once every 3 months ? IS there a ground I am missing ? ALL GUAGES WORK BESIDES THIS
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1969 BBG,BBO, BBB/ 1970 Machine - www.bigbadamx.com
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amcglass
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Joined: Dec/11/2011 Location: NW Ohio Status: Offline Points: 2588 |
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Posted: Jun/17/2018 at 8:40pm |
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would think it is a ground issue
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Javmanpres
BBG Mark Donohue 401 74 Jav/AMX 71 Matador 2dr sedan delivery wagon 1902 Rambler Runabout 70 T/A Javelin |
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mmaher94087
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Joined: Apr/01/2008 Location: Arizona Status: Offline Points: 1690 |
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Posted: Jun/17/2018 at 8:50pm |
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Yes. Sounds like a ground issue. The '69 tach built into the cluster will allow one to drive the car even if the tach is burned out. The '68 Tach will not. Check your grounds for the cluster.
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Mike
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Trader
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Joined: May/15/2018 Location: Ontario Status: Offline Points: 6881 |
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Posted: Jun/17/2018 at 9:13pm |
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After checking the grounds, with the engine running, put your hand up and give the main instrument harness connector a wiggle and see if anything changes.
Don't have the rally cluster but mine did have a board pin loose in the cluster. Intermittent on off gas and temperature gauge from the same power supply. Had to take the board out and solder the pin to the board to ensure good electrical connection - did all of them since I was in there.
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musictoyz
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Joined: Apr/17/2012 Location: cumberland, me Status: Offline Points: 377 |
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Posted: Jun/17/2018 at 9:35pm |
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Trader....I am pretty sure the 69 run totally on its own 2 wire harness...you are correct that pin connector can give you a bunch of headache...
I took the cluster out...I took the tach out...and open it. Yes thats how tired I am of this....the tach has a mini transformer to knock the 12 v down ...there is 4 caps, 2 resistors and a magnetic thing that is connected to the dial.. looked around... cleaned terminals... hooked it...it works But it jumps all over... So I think I am gonna call a tach guy tomorrow...see how much, if crazy $ may put in new caps etc
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1969 BBG,BBO, BBB/ 1970 Machine - www.bigbadamx.com
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Rebel Machine
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Posted: Jun/18/2018 at 6:21am |
You are correct, the AMX tach does not use a ground. It's inline with the power feeding the ignition coil. I'd think if there was an intermittent connection you'd have a misfiring engine. -Steve-
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Trader
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Posted: Jun/18/2018 at 9:58am |
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Yes the tach has a separate connection - my mistake. Just finished a Ford that had an intermittent tach and put that together with the 69 Javelin temperature/gas gauge problem.
Too many vehicles with intermittent electrical faults in the last few months! Including the brain. |
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musictoyz
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Joined: Apr/17/2012 Location: cumberland, me Status: Offline Points: 377 |
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Posted: Jun/18/2018 at 10:43am |
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I know and they can drive this old brain crazy !
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1969 BBG,BBO, BBB/ 1970 Machine - www.bigbadamx.com
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musictoyz
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Joined: Apr/17/2012 Location: cumberland, me Status: Offline Points: 377 |
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Posted: Jun/18/2018 at 11:43am |
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Welllllllll it seems I didn't even know the addition of Pertronixs II would create such havoc.... Anyone know of the conversion to the tach for Pertronixs...everyone wants $299 for this repair/convert yikes ! |
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1969 BBG,BBO, BBB/ 1970 Machine - www.bigbadamx.com
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PHAT69AMX
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Joined: Jul/07/2007 Location: West Virginia Status: Offline Points: 5919 |
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Posted: Jun/18/2018 at 3:27pm |
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Don't know what it takes when using PerTronix...
But when I used a UniLite and an MSD Box, this is what it took to make stock tach work...  |
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musictoyz wrote: