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Re: [Healeys] Fw: Possible explanation on the Petronix

To: Bob Brown <blkbt7@yahoo.com>
Subject: Re: [Healeys] Fw: Possible explanation on the Petronix
From: Bob Spidell <bspidell@comcast.net>
Date: Tue, 10 Jan 2012 23:48:24 +0000 (UTC)
Unless Pertronix has changed the Ignitor design in the 8-10 years since I 
installed mine, it will work with a Smiths electronic tach on a pos-ground car. 
Mine works fine and, in fact, since I calibrated it is absolutely spot on 
accurate and stable. Hard to believe, I know, but it is as verified by my Sears 
dwell-tach and by inference with the GPS/speedometer/gearing/etc. 

All I recall doing was reversing the loop formed by the white wire on the back 
of the tach, but I might have rerouted the white wire. Sorry, I don't have a 
schematic, but the thing to think about is the Ignitor switches battery current 
to the coil--you have to provide an alternative ground to the coil (I used the 
notorious battery cutoff switch and white/black coil ground wire moved to a 
different terminal on the switch)--whereas points make and break a circuit to 
ground from the coil. The tach is probably (has to be) wired in series with the 
coil and the points, so you may (probably) have to change the routing of the 
white wire. I did not remove any wires from my harness; just rerouted them so 
that I can easily go back to points in an emergency. 

The loop on the back of the tach is an inductive pickup. If switched current 
flows through the wire--with the proper polarity--the tach will work. The 
needle on the tach moves in proportion to the frequency of the current pulses. 
Not that I doubt a reputable outfit like Nisonger, but the Ignitor I ('one') is 
hardly more than an electronic points set (with some inductive-capacitive 
circuitry to even out 'dwell'). 

Bob 


-------------------------------- 
Bob Spidell - San Jose, CA 

----- Original Message -----

A club member recently installed a Petronix ignition in his positive ground 
BJ8, 
Car fine s fine but the tachometer does not operate. This is of course 
because 
it is not connected. 


Several attempts to wire to operate the tach 
ahve proven unsuccessful. He has 
talked with Petronix tech support but they 
could not provide a definitive 
answer. I'm sure there are many positive 
ground BJ8's in the owrld that have 
properly functioning tachometers. What 
is the wiring?? 


Our club member sent me the following, which he now 
believes to be his best and 
possibly only option. I'm sure Niosonger knows 
more about this than I do but I 
have never heard that a paoistive ground BJ8 
tach will not work unless rebuilt 
as they state. A fair amount of cash has 
recently gone into this car and I hate 
to see him spend more needlessly. 

Any 
comments? 

Bob 


"I spoke to the owner at Nisonger Instruments. They rebuild 
the Smith 
gagues...Anyway...I mentioned I was going to sen him my tach and 
speedo for 
rebuilding this winter...he casually asked about if I had 
converted to 
electronic distributor...and the truth came out. The Petronix 
he says is not 
compatible with the loop tach style Smith gauge. So they can 
rebuild the 
tach...to look authentic, but add electronics. See link below. 
He said they 
rebuild a few hundred a year like this. Not sure why it is not 
common 
knowledge. 

So as you saw with my car...if you wire the coil and 
distributor as Petronix 
instructs...it works fine...you do have to remove the 
wires from the harness 
that used to terminate at the coil. But apparently 
you no amount of tweaking 
will get the old tach to work." 

http://www.nisonger.com/electric-tachometer-conversions.htm 
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