Tach problems with Mallory Ignition Control

[BarronTG]

I have installed a Mallory Hyfire VIAL Series Ignition Box (PN 6853M) in my '72 02tii and cannot get the tach to work. I am using a Mallory UNILITE distributor. I used the yellow tach wire coming out of the box but it doesn't make the tach work. The manual that came with it said if the tach doesn't work with the yellow wire alone, an adaptor (PN 29074) will have to be used. I'm not sure that the adaptor would even help. But before I purchase this part, I was wanting to make sure that there was anything that I could do or shouldn't do before. Is the voltage on the tach wire coming out of the box supposed to stay a constant 12v? This one does. I'm not sure but I just assumed that the volts would vary depending on the rpm's. Any help on this would be greatly appreciated!

[uxoman]

The adapter should make it work. I had to use one on my MSD ignition set-up.

[BarronTG]

Awesome! Now I can order the adaptor without wondering if I'm wasting money. Thanks so much!