Bob - it might work for a GPS unit but that switched DC voltage line has a fair amount of noise on it, and some GPS units do not deal well with the noise (insufficient filtering ontheir DC input) as many of these devices expect a cleaner DC power source like from an automobile's power jack. Some GPS units will work OK connected to that point, but some may have to be connected directly to the battery on these old bikes. Voltmeters, etc. are basically oblivious to the noise on these lines, as they don't have fancy-schmancy microprocessors in them.