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| Joined: | 03-12-2005 |
| Location: | Kingman, Arizona USA |
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http://www.msdignition.com/pdf/8920_frm22049.pdf .
First of all, verify that the MSD main box, MSD adapter, and Pertronix gadget are all connected exactly as shown on the second page of the instruction sheet, the one that applies to current-mode tachs like the one used in the JH. Note that for the Pertronix, the black wire is the trigger, and the red wire goes to switched power. I'm not sure how this is supposed to be done when an MSD box is used, but I'd imagine that their paperwork will explain things. If not, try the wire from the ignition switch.
Note that the power for the MSD boxes comes directly from the ignition switch and does not run through the tach. Probably the easiest way to provide this power is to splice into the white wire that runs from ignition switch to tach (NOT the wire from tach to coil).
The MSD coil is connected ONLY to the two wires from the main box. The ballast resistor is no longer required, and the wire from starter solenoid to ballast / coil should be disconnected and taped off, or even removed.
Once all this has been done, the car should start although the tach will not yet work. If it doesn't run, then the MSD main box, Pertronix, or coil is bad, or something is not yet hooked up correctly.
Once the car runs, verify that the tach has power on both its Green wire and the White wire from the ignition switch. The remaining White wire will remain connected to the tach as before. However, the engine bay end of this wire, which used to go to the coil, will now instead connect to the tach control wire from the MSD adapter box. The tach will then be driven by the MSD adapter box, which in turn is controlled by the MSD main box, which in turn is switched by the Pertronix device.
If you've done all the above, the tach should work correctly. If not, call the MSD support line and explain the problem. If they don't have a simple fix, or if it doesn't work for you, it's likely the tach's internal electronics have degraded due to age and the tach will need to be overhauled by a competent specialty shop, which will need to know the details of your situation. Alternately, for roughly the same money, you could have your tach's internals replaced with more modern electronics, or install a voltage-mode tach such as those made by VDO.