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Originally Posted by Canucklehead
I have to disagree with your diagnosis here. A bad or missing ground is going to prevent a component from coming on, therefore it won't be a current draw. A battery that won't maintain a charge overnight has some load on it which would indicate a switch or relay or something sticking shut.
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I didn't say his reading indicated a current draw. Measuring voltage from battery negative to a point that is supposed to be electrically the same point should give a reading near zero volts. The engine should be connected to battery negative (grounded) essentially being a piece of wire in a circuit. You shouldn't be able to read a voltage drop across a wire with no load. There are other issues here besides a draw on the battery.
Switch your meter to the amp setting and disconnect the negative battery cable. Remember to switch your positive lead to the amp jack on your meter and then, with everything off in the truck, place your meter INLINE between the negative terminal of the battery and the end of the battery cable. This is how you read current in a circuit. Mind you, if you think that the current draw is over 10 amps, don't try it. Most common meters won't read more than 10 amps. One way to test, before you fry your meter, is to place a 10 amp inline fuse between the neg terminal and the negative battery cable. If it blows, don't use your meter to measure the current draw. Or, if you happen to have an inductive amp clamp, you can do it without removing the battery cable and safely measure several hundred amps, depending on the amp clamp.