I'm not sure I understand that question.
Using the voltmeter from battery terminals to frame will usually give false results.
The truck frame must not have any current at all. If you have a dirty battery, where corrosion is between the frame and battery, current will flow. Raymond says to use an amp meter from positive then negative to frame. One miiliamp can cause problems. I've seen trucks at 100 milliamps that caused major damage to computers or drive amps. Before using a amp meter, try a 12 volt test light first. If it lights even for a second, dont use amp meter as it will burn the fuse. Use a 5 amp fuse in line to protect your meter. Check the truck for shorts as well. unhook bat, use ohmeter at truck connecter pos then neg, to to frame. Should be at least over 100 K ohms but normally 1 meg. Check the static strap with ohmeter on strap end then to frame. Need to see 10 thousand ohms. If open, the resister is blown.