There is a problem with 102C3s and other 102s that has to do with the tripple 7 safety switches, that was corrected on later numbered chassis, with a 2 part kit, and new regulator part, expensive.
My not gen light flashed on and off, sometimes the check starter light came on with it, causing no alternator charging, killing of my tachometer, which is run off the back of the alternator. It did this for awhile, just lasting seconds, my mechanic couldn't find it, till it stayed on and exposed this factory design fault, there's a by pass for just a short time, but it can cause issues, if you leave the batteries on while engine is not running, according to Stewart and Stevenson knowledgable mechanics.
The drop from 28 volts to 24 volts is the alternator not charging and just batteries supplying power to whatever 24 volt electric draw is going on...lvmci...
