I have both a Lowrance 540c and Lowrance 7200 in the race truck wired to the same power source. The problem is the 540c will turn off when the starter is engaged while the 7200 will remain on. Both units are wired identically and I can find no reason why one turns off and the other doesn't when starting the motor. Is there a setting within the GPS unit menus to fix this or is this how the 540c is supposed to operate? Any help would be great it is starting to get annoying.