There will occasionally be enough voltage sag when the machine is being started, that the GPS will either reset or partially reset and be flaky due to too low voltage. We were having that problem with the combine so I took time to hook a diode in-line to the small AGM sealed battery, that keeps it charged and normally supplies the GPS unit and relies on the small battery to keep starter draw from pulling the voltage down. The small starting battery on our DR-trimmer mower gave out this spring and I ordered a spare that got used for this.

The 500 has been powered by a dedicated wire running to a cigarette plug. The wire attached to that with a spade terminal. Shown here, the spade hooks into the existing socket that supplies 12V. The socket wired to the battery side of the diode hooks to the lighter plug in this configuration. The black wire on the neg. post of the small battery is grounded to the combine frame.