I wired a new GPS speedometer (figure) and faced a some kind of interference problem (I guess) while starting my 70 hp Yamaha. There is now a constant voltage (12 v) from ignition switch to speedometer (when turned power on). At this point everything is OK, speedometer gets power, GPS founds satellites in reasonable time. Then, when I turn the ignition on, the speedometer gets frozen, but power is still there. This happened most of the times I turned the ignition on, but few times everything remained good after the ignition (as can be seen in the figure). Maybe I should give power to the speedometer after the ignition with a separate switch? All the advice is appreciated.