Tach issues with MSD 6 Hemi

So is anyone out there running an aftermarket tach with an MSD 6 Hemi box? I have a little Actron Acrotach I got at a swap meet and like the small form factor, but when I hooked it up to the 12v yellow tach line from the MSD box I'm getting nothing out of it. I know MSD sells a bunch of different tach adapters for different setups, but I was wondering what other people had done. The tach adapters are almost as expensive as a new tach anyway, so if I just need a different tach I may consider that.