240Z Tach topping out to 8K whenever key is on

[chocolate_supra]

Title says it all. I've got a 72 240Z with a tach that tops out as soon as the key is turned to the on position, start position, and while the engine is running. Only way to stop it is to turn the key off. Pretty sure it's the tach itself and not wiring, etc because I just went through a bit of a situation with my ignition during which I tested and found the entire ignition circuit and every component to be perfectly fine. I'm about to pull the dash to replace the lights and would like to fix the tach, too. Any advice on what to look for and replace when I get the tach out and apart?

[EScanlon]

Yes, replace the tach.

You shorted it and that fried part of the internal circuitry.

E

[chocolate_supra]

I'm not looking to replace the tach, looking to fix it. Was wondering if anyone has ever had the same problem and fixed the tach itself.

[tlorber]

I tried measuring resistance on each (11 of them) in my '73 tach. I even tried replacing 2 of the resistors. Ultimately, since I wanted to keep the original tach I had it rebuilt. They basically replaced the entire guts with modern solid state. It is more accurate than the original was, and will accept a signal from either the original distributor , an electronic dizzy, or pertronics type ignition. It looks original but is dead on as compared with a timing gun. It cost me $175.00.

[Arne]

This is a fairly common problem, but I've never heard of any successful repairs. As far as I know, it's either replace with another, or replace the guts as noted above.

[Gary in NJ]

If you do decide to replace the tach, keep in mind that Datsun used several different wiring schemes over the life of the S30. Know what you need before you buy.

[chocolate_supra]

Having it rebuilt with solid state sounds attractive. Where could I go to get that kind of work done? I'm in the Fresno area, but I wouldn't mind boxing and shipping the tach.

[tlorber]

I had mine done here.

http://www.nhspeedometer.com/

They do nice work.

[260 z]

Chocolate supra...I am restoring my 260z after it sat for 26 years and just got it started yesterday. My tack is doing the same thing. If you repair or replace yours, will you let me know??

[ajmcforester]

I got a NOS, but the original looks just as good, but is doing the same thing. I plan to take it apart, great EDU time I might to this after the car is back together, unless someone knows how to repair it.

[chocolate_supra]

@260 z

Wow! I'm sure that Z is enjoying the new attention! I'll certainly let you know how it works out whichever path I take with my tach.

[chocolate_supra]

By the way, I just accidentally found this:

http://www.dinoplex.org/tachoconversion/index.html

but it looks like the final product is meant to work only with electronic ignition systems, which I'm not doing (yet). Has anyone seen any instructions like this on how to convert the tach to solid state that's compatible with the factory ignition? My dad knows electronics and we could put it together with instructions like this. Looks like fun, actually.