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DO I HAVE TO USE A RESISTOR TO INSTALL THE STANDARD 240Z TACHO?


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#1 Hunter

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Posted 19 October 2008 - 07:44 PM

This is a tachometer off my 1973 Datsun 240Z. I am turning the car into a race car, so I have no need for the factory gauges anymore. This tack works perfectly fine and is also in excellent shape. There aren't any crack or chips in it and no missing parts. This tach is factory, so it will only work with regulated points ignition systems. It won't work properly with an electronic ignition without installing an aftermarket resistor. The tach should fit in any 1970-1973 Z dashboards, but I'm not positive on that. Fell free to message me on eBay or call me with any questions you might have. (714) 606-1229 and ask for Mike. Happy bidding!


The above is a quote out of a ebay auction. Currently I have a Monster Tacho installed in my 240Z. I have a electronic dizzy and have a coil that does not use a ballast resistor.

Do I have to install a resistor to make the original 240Z tacho work correctly?

Sorry I do not have clearer pics I will try and get some better pics later.

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#2 reverendzed

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Posted 19 October 2008 - 07:51 PM

Hey Hunter, Talking to Scootag yesterday about my electronic dizzy and he pointed me to this site http://www.datsunzgarage.com/engine/ which if I recall spoke about this exact issue.
Hope it helps.
Rev.

#3 Zedman240®

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Posted 19 October 2008 - 08:55 PM

When I had my L series engine and electronic distributor I ran the original tacho and no ballast resistor with no issues. The 240/260 tacho's are triggered from the positive side of the coil i think.

#4 Hunter

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Posted 19 October 2008 - 09:11 PM

Dimitri I are you sure it is not the negative side?

I will do some more reading.

#5 Hunter

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Posted 20 October 2008 - 04:16 AM

Awesome link by the way rev

#6 modular9

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Posted 20 October 2008 - 08:19 AM

yes

I have a l28 electronic dizzy and a late 260z tacho. I have tried a crap load of things and the only thing that worked was to put the old points based coil and ballast resistor connected to the elec dizzy. not good as the spark was *$%^$% so at present i run with the tacho disconnected.

Cool thing was that i ran across a hybridz thread where someone detailed exactly the 10 k resistor mod. SO that is on my list of todo things.

Also there is a post somewhere on the net about someone called nzeder ( i think he is on this site as well ) who got a gauge guy to swap the internals or mod them with some smith gauges internals .
ALSO I ran a multimeter on the positive side of the coil and that is definitely the side that is sending the signal. I traced it to the interior and the mulitmeter works just not the tacho !


#7 Scoota G

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Posted 20 October 2008 - 08:41 AM

My tacho work exactly the same as it did before i put in the Electronic ignition but even before it did play up and didn't show the right revs. it still does it sometimes.

#8 PZG302

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Posted 20 October 2008 - 01:58 PM

To get the 240 tacho to work with electronic dizzy this is what you need to do....

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#9 Hunter

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Posted 20 October 2008 - 05:31 PM

Where is the IC ignition box located?

#10 Scoota G

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Posted 20 October 2008 - 05:42 PM

That is usually the one on the side of the electronic distributor.

#11 Hunter

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Posted 20 October 2008 - 05:44 PM

I thought as much, I will check it out tomorrow. I have 6 days off.

#12 crowe

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Posted 11 May 2009 - 01:51 PM

Hey Hunter, how did you go with all this.

Did you find a solutions to your issue?

An update would be great as I am having similar problems with the tacho and electronic ignition and interested to see how you went.

#13 Hunter

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Posted 23 February 2010 - 09:41 PM

sorry for the late reply. The tacho started working, but keeps blowing a fuse.

I am sure it is a electrical short somewhere.

#14 NZeder

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Posted 24 February 2010 - 05:05 AM

Spotted my username mentioned in this thread. Yes it was me who had a smiths agent install a new board in my tach. This board is a smiths old jag tach upgrade. Basically the zed tach is licensed copy of the old smith tach. That means it is connected to the positive side of the coil and tach is driven by an inductive loop.

Others have gotten the stock tach to work with EI me I wanted to have my work like a modern tach and connect to the negative side and at the sametime he check/adjusted it so it was showing the correct revs.

I believe the board he installs is from Australia. I am now upgrading all my gauges so my 260z mod tach could be forsale (260z tach have a different font than a 240z)

#15 Hunter

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Posted 12 March 2010 - 05:40 PM

NZeder I have noticed you in a few posts on HybridZ with the Speedhut gauges. I have just upgraded my engine to a RB25det.

I am looking at getting a full set of Speedhut gauges myself, is this the way you will be going? Also for the smaller in dash gauges are you going 2"5/8th or 2"1/16th.
I noticed there is two setups on there one with black bezel rings and one with silver bezel rings.

SE PICS BELOW
Black Bezel 2"5/8th and Silver Bezel 2"1/16th

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#16 Timwell

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Posted 18 March 2010 - 09:46 PM

isn't the ballast resister only used to stop over voltage of the ignition circuit when cranking the engine?

#17 stevo_gj

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Posted 18 March 2010 - 10:23 PM

isn't the ballast resister only used to stop over voltage of the ignition circuit when cranking the engine?


Pretty sure its the other way around. The ballast resistor is bypassed only when starting the engine, but is in use the rest of the time to prevent the points getting worn.

#18 Zedman240®

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Posted 19 March 2010 - 07:34 AM

When cranking the engine, coil gets a full 12V (stonger spark to help start), while running coil only runs on approx 9V like Steve said to prevent point meltdown.




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