View single post by Mark Rosenbaum
 Posted: 02-19-2006 07:58 pm
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Mark Rosenbaum



Joined: 03-12-2005
Location: Kingman, Arizona USA
Posts: 532
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 It probably does matter which way the two white wires go.  While it seems unlikely that you could damage a tach by reversing the connections, it probably wouldn't work right, or might read incorrectly.

With that in mind, I just took a glance at the wiring on my car.  On it, the white-slate wire goes to the ballast resistor.  Therefore, the male pin on your tach should connect to a high-current (about 8 amps peak) +12 volt supply, and the female pin on your tach should connect to the ballast or coil {+} terminal.  This should replicate the way the factory plug is connected.

Bear in mind that some JHs and/or GTs used a ballast wire instead of a ballast resistor.  I've never actually seen a car with this arrangement, and consequently don't know how they handled the ballast bypass wiring from the starter.  Possibly they would have just left it unconnected.

You should also be aware that some owners have reported that their tachs don't work after they install a Pertronix device.  AFAIK no one has ever taken a close look at this, so it's uncertain why it occurs, but perhaps the tachs in question were marginal, or it may be related to the coil used.  I would not think it at all likely that the Pertronix gadget itself was the culprit.