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Since I was able to get a Pertronix to work with my BJ8's tach a
lister asked for details on my install. Last I heard, converting an
electronic tach for use with a Pertronix costs $200-300, and the
'do-it-yourself' instructions are fairly complex, so I'm passing
this along for general information.<br>
<br>
<b>Disclaimer: This worked for me; maybe there's a 'trick,' or maybe
I just got lucky. I did calibrate my tach once--to an external
tach/dwell meter and confirmed with radar/gear ratio
calculations--but I don't recall that it was related to the
Pertronix install.</b><br>
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In the engine bay, the white wire (12V) is spliced to the black
lead from the Pertronix--pos. gnd. car and Pertronix--and the
black/white striped lead goes to the -/SW terminal on the coil
(the coil will work either way, but puts out a bit more voltage if
it's properly wired). Note the Pertronix switches current to the
coil 'upstream' of the coil, whereas points switch the current to
ground 'downstream' of the coil. The white/black wire from the
+/CB terminal on the coil is the ground; when the cutoff switch is
in the 'on' position the coil is connected to ground, whereas on a
points system the wire is switched to ground when the coil is in
the 'off' position (current is shunted around the coil). You can
switch the two small leads on the cutoff switch to accomplish
this; I used a large ring crimp terminal as one of the terminals
on the switch is larger than the other.<br>
<br>
It's been years, but IIRC I had to cut the spade lug on the
ignition switch in order to route it through the pickup. If you
want, you could cut the wire, temporarily splice it together as
you try out different routing, then permanently splice them
together (the ignition switch on a BJ8 is a PITA to get to, you
have to pull the console).<br>
<br>
The underdash photos show the inductive pickup on the tach. I
forgot about the little 'clip' the wire goes through, that may be
part of the secret to making the tach work. The white wire in the
foreground is ganged-up on the ignition switch on the 'run'
terminal, the other half of it goes into the wire loom and comes
out as the white wire I've spliced to the Pertronix black lead in
the engine bay.<br>
<br>
I've included the schematic from the shop manual in case you don't
have it. Remember not to leave the key in the 'run' position with
power for more than a couple minutes; it will fry a Pertronix
(Pertronix II/III have protection from this, but last I checked
with Pertronix--about a year ago--they don't make the II/IIIs for
pos. gnd.).<br>
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