Alright, I've got another strange one. I have a digital Voltmeter added to the Muddog, (2002, 4.0, 170,000 miles), and in warm weather it's always shown 13.9 volts. Yesterday, it was displaying 13.5-6 volts. This morning, 14.1-2 volts. Later, back to 13.9. It's never done this before. Is this an...