Wow, I'm glad I posted this question. I'm tending to go with the capacitor theory since the voltage continued to drop. I read it yesterday afternoon at 0.1 v and I'm testing with the batteries completely disconnected from the truck. I'll check the pH of the coolant and will see if I can read any charge from the coolant itself. I'm having a hard time wrapping my head around how a radiator acting as a battery could put current into the electrical system of the truck, like at the cigarette lighter. With quite a few years on the coolant but only a few thousand miles, it's probably due to be changed anyway. pH should tell me something about that. I'll check my meter on a potato. I think there's one still in pretty good shape out on the compost pile and maybe one still in the house. We do have some good sweet potatoes. Thanks y'all!
'94 K3500 Silverado DRW long bed crew cab 4X4 with most of the options
Bought on 3/23/11. Current mileage 161,805
It came with new 6.5L TD Goodwrench crate motor dealer installed at 99k miles and 4L80-E trans rebuild at 135k miles
G80 4.10 rear, 225/75 16 tires
New Stanadyne FSD on 3½x6x1 aluminum heat sink, remote mounted above and behind the bumper.
Heath Turbo Master, Hayden SD fan clutch & trans cooler
Diamond Eye 4" exhaust, GlowShift diesel combo gauge. Analog EGT, Digital Boost & Trans Temp