I would do like Ed suggests with calling powermaster.
I do question, on a 68, the original setup is for an external regulator and this new powermaster alternator you installed, is it made to work with the old original external regulator, or was a new external regulator supplied or is the regulator built into the new alternator and the old original external regulator needs to be removed and/or other wiring changed and/or upgraded ?.
I wold also double check your connections.
While the ignition system may like the 16.6V, the cars lighting system may not so don't run it too long or at all at this high voltage.
On a high output Lestek alternator I have, it has an external regulator that is adjustable to where I used it in stereo competitions and it allowed me to have anywhere from 13V up to around 18V. If the powermaster setup you bought came with an externally adjustable regulator maybe this needs to be adjusted and if so Powermaster should be able to tell you the procedure.
A forum community dedicated to 1st generation Chevy Camaros owners and enthusiasts. Come join the discussion about performance, builds, restoration, modifications, classifieds, troubleshooting, reviews, and more!