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Thread: Tachometer not working

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    Default Tachometer not working

    I have a 73 240z, my tachometer does not work, i have checked all the wires around the ignition coil, i have a spare tach i do not know if it works though, but i tested it directly on the coil and could not get it to move at all, i do not know which wire i should be looking for on the coil it seems as though there are more than the 2 that the manual idicates, help would be awsome, thanks.

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    Registered User zeiss150's Avatar
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    did you change your dizzy or coil at all? If you bypass the ballist resistor your tack won't work. If you hook the tack up to a 12volt source I think (and I could be wrong) it will fry the tack. I believe that the ballist resistor limits the output to the dizzy to a little over 6 volts. Other than that I can't help you, sorry.

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    Not quite true. I have no ballast resistor in my 240Z ('71 with ZX dizzy), and my tach works just fine, thank you.

    But the first question above is very relevant. What type of ignition do you have on your car?
    Arne - Former owner, HLS30-37705, 7/71, 905 Red
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    A ZX dizzy is designed to be run without a ballast resistor.
    Last edited by sblake01; 05-29-2006 at 08:29 PM.
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    Registered User zeiss150's Avatar
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    I have the dizzy and coil from an 81ZX on my 72 240 it bolts right on just take the dizzy collar from the zx eninge, and i'm still using the ballist resistor. I was told that the tack ran through the resistor and that if you didnt use it it wouldn't work. bad info I guess.
    P.S. I had to rebuild the dizzy, but once you put it on its a great upgrade, oh and don't forget the 70 amp altinator upgrade from the zx turbo engine, its a must!

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    i know i have an ignition coil, and i believe its the orignal one that was on the cars sold in california, i basically want to know how i can test my spare tach off the coil to see if it works, and if its a problem other than the tach, i am trying to trouble shoot if its a connection, wiring or the tach it's self

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    Quote Originally Posted by Skotty
    i know i have an ignition coil, and i believe its the orignal one that was on the cars sold in california, i basically want to know how i can test my spare tach off the coil to see if it works, and if its a problem other than the tach, i am trying to trouble shoot if its a connection, wiring or the tach it's self
    The tach used in the 240 is of an induction loop type. That is, the power comes from the ignition switch, thru the tach, and powers the coil. The tach "reads" the inductive pulses created by the coil firing. Easiest way to see if it works, just replace the old with the new....takes about 15min to do.
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    to change the tach do i have to disasemble the dash or can i simply disconnect it from behind the dash?

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    Master of Weaponry Dtsnlvrs's Avatar
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    Quote Originally Posted by Skotty
    to change the tach do i have to disasemble the dash or can i simply disconnect it from behind the dash?
    There are two wing nuts that attach the tach to the dash, and of course the wiring harnes stuff. Remove the nuts, then push the tach thru the opening (toward the driver).
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    I've got the exact same problem, '73 240 with 280zx efi motor no balist resistor does anyone know the colour of the tach wires at the dizzy and if +ve or -ve. thanks

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    i saw those wing nuts, the spare tach i have may be out of a later model it has this braket comming off the back and the plastic shell has a hole for a screw to go through it would it be possible just to take the tach off that mount and put it on the one that is in the car?

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    Quote Originally Posted by Skotty
    i saw those wing nuts, the spare tach i have may be out of a later model it has this braket comming off the back and the plastic shell has a hole for a screw to go through it would it be possible just to take the tach off that mount and put it on the one that is in the car?
    Nope, if it is off a later model car it is not without some wiring modification. Best bet is to find another tach, or double check all your wiring per the factory diagram. Make sure all your connections are clean etc. New tachs can still be found, but better make sure that is the problem first.
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    As I understood it, and I could be wrong on this, but the purpose of the ballast resistor is to reduce the voltage going to the mechanical points on earlier cars to reduce the likely hood of frying/burning them, and nothing else. I believe it reduces or basically halfs the voltage going to the points.
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    i took apart the spare tach and there are 3 wires. Are those the modifications i would have to make? By connecting the negative and positive to the orignal mount as well as the singal wire? because the actual tach is the same just a different harness is it not?

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    The brackett coming off the back is from the 73 and later I believe. My 72 just has the 2 screws and it doesn't work. Thinking about geting something aftermarket. Any suggestions?
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    i have a 73 and mine just has the two wing nuts on the back holding it in place, but i would like to know if the wiring modifications i have to make are just the negative postive and signal wires

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    Quote Originally Posted by Skotty
    i have a 73 and mine just has the two wing nuts on the back holding it in place, but i would like to know if the wiring modifications i have to make are just the negative postive and signal wires
    I am not sure, as I have never tried to install a tach that did not "plug and play" Try finding a tach that will plug and play, call around to different Z shops, see if any have a used tach lying around.
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    okay thanks alot for the help, it was greatly appreciated

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    I began removing the tachometer and i realized that the signal wire was not even hooked up, infact is was just rolled up and tied to the dash, great all i have to do is hook it up right, i know that the green wire goes to the positive side on the coil, and that the black wire goes to a resister and then to the ignition switch my question is where is the hook up on the ignition switch and where is the resister that i must through?

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