Tach Problem

I hope someone can help me, my problem is that the factory tach does not work since I upgraded my ignition system. My 69 Camaro, V8, factory tach,
factory tach wiring harness, point style distributor and stock coil worked fine before the upgrade. Upgraded distributor to Mallory Unilite, upgraded coil to Mallory Promaster and added in a Mallory Hyfire IVA ignition control box. Everything is wired and connected fine (per instructions from Mallory) and engine runs great. I tried wiring same as factory (lead from tach to coil negative side) and the tach did not register anything, switched the lead to positive side of the coil and the tach reads about 800-1000 rpm too high! Question is - How do I properly wire the tach for this set-up?
This is as far as I want to go with trial and error as I do not want to fry anything!
Thanks in advance for the help:)
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