My Balmar MC-612H will be 10 years old in September. It has been very reliable during that time, regulating a 100-amp Balmar alternator on my Perkins
It, too, is installed in a cool, dry location with lots of air. That's important.
Only once did I have a problem: for no apparent reason it lost
its program, and was on P0. This was quickly remedied as soon as I noticed it.
I have installed a bunch of these on client's boats, and have a couple of new backups which I have never had to use. I've heard of several failures of the AR-5 regulators, but the MC-612 series seems pretty robust, PROVIDING that you don't install them in the engine
One problem they do have: the in-line fuses
and the manner of connection to the blades are a trouble spot. Sometimes with those Buss fuses
even though they might check OK with a high-impedance multimeter, they can't handle the amperage. And, they're always susceptible to surface corrosion
, so keep 'em very clean. I've replaced mine with better blade-type fuses.
I didn't quite understand what you meant by, "but you cant enter the modes". Do you mean the magnetic wand doesn't work? Again, I'd check the wiring, not only at the regulator but also the voltage sensing and field control wiring at the batteries and alternator.