Hi guys. The alternator can't cause this on its own unless something very unusual happened to the brushes inside it. This can be caused by a shorted voltage regulator inside the Engine Computer but due to the circuitry, it is very unlikely the voltage will go that high. To reach 26 volts the control wire between one of the smaller terminals on the rear of the alternator, and the Engine Computer has to be grounded. That will be the green / black wire. Also, even if it's grounded, the voltage won't go much above 16 volts at idle. You would have to raise engine speed to reach a higher voltage.
My first guess is you're reading your voltmeter incorrectly or it's giving you an incorrect reading. 26 volts will kill the computers on the truck and any light bulbs that are turned on. You'd have a pile of symptoms. What exactly are the symptoms and how did you get that voltage reading?
Tuesday, October 7th, 2014 AT 2:07 AM