[Healeys] Fwd: Tach rebuild

[Bob Spidell]

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.

*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.*


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.

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).

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.

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.).




-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://autox.team.net/pipermail/healeys/attachments/20201127/e144ffbb/attachment.htm>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: Coil.JPG
Type: image/jpeg
Size: 701523 bytes
Desc: not available
URL: <http://autox.team.net/pipermail/healeys/attachments/20201127/e144ffbb/attachment.jpe>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: TachCoil.JPG
Type: image/jpeg
Size: 627264 bytes
Desc: not available
URL: <http://autox.team.net/pipermail/healeys/attachments/20201127/e144ffbb/attachment-0001.jpe>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: Schematic.JPG
Type: image/jpeg
Size: 728088 bytes
Desc: not available
URL: <http://autox.team.net/pipermail/healeys/attachments/20201127/e144ffbb/attachment-0002.jpe>