View single post by edward_davis
 Posted: 01-17-2008 06:03 pm
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edward_davis



Joined: 07-06-2005
Location: Eugene, Oregon USA
Posts: 162
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 From what I understand a certain number of the tachs just won't work with the pertronix.  For starters, the JH tach works differently from all modern tachs, in that it reads pulses in the ignition wire that goes to the coil, instead of reading the "other" post of the coil.  So the waveform the pertronix makes is different enough from the standard points-type distributor that some of the units just can't read it. 

You could also have a broken tach, like I did a year or so ago.  You can check continuity inside, to see if there is a break somewhere in the circuitry; mine had a broken connection somewhere in the coil of wire that drives the needle.  It's an easy fix, though: buy an early 70's MGB tachometer on ebay and substitute its works.  Not too tough, since it has the same redline and the mounts for the face and case of the tachometer are the same.  There are also several gauge repair shops that will sub in a brand-new tach's guts, so you can keep the look stock.  You'll have to rewire, but it'll be more precise and more accurate, too!

Edward