[G.M.]

The problem is when running off 6 volts at very low speed and at idle the cutout on top of the early generator and in the voltage regulator on later 6 volt engines disconnects the generator from the battery. Now you are running the GPS off the battery. The battery voltage is about 6.3 and is right on the minimum voltage required to power the GPS. As John reported if you touch the brake the power drops when the brake lights come on and the GPS drops out just when you need it in a strange town. It takes a little time to bring the GPS back to where it works again. With the little 2.5" square box that converts 6 to 12 volts you don't have the drop out problem. These are usually available on eBay for $55.00 to $80.00. I also always carry a 12 volt jumper pack with an air compressure, 12 volt lighter plug and 110 AC output. I have a jumper pack with a switch that disconnects the jumper cables. With this switch you can hook the 12 volt cables to the starter and ground, have someone turn the ignition on and then actuate the jumper cables and it starts right up without 12 volts through the whole system. G.M.