Honda BF20A-BF25A, BF25D-BF30D Outboard Motors Shop Manual., Page 372Get this manual
D-GPS INSTALLATION PRECAUTION NOTE: Carefully follow the installation instruction when install D-GPS1) Keep the D-GPS unit and antenna at least (10 ft)
METER WIRE HARNESS CONNECTION
Route and connect the wire harness properly as shown in the wiring diagramUse the genuine Honda wire harness and modify it if necessaryNOTE: Stake the lead wire against the terminal securely using the special toolUse the 1.25 mm (0.05 in) dia(AWG #6) lead wire to put them togetherSolder the joint section and protect it by wrapping with piece of insulation tape
away from the outboard motor
2) Be sure to connect the ground system to the boat
INSTALLATION
Meters and other instruments should be installed on the dash boardIf any other location is selected, it will be necessary to use mounting plate with thickness of11 mm (0.040.44 in)NOTE: If the mounting plate thickness exceeds 11 mm (0.44 in), the bracket must be modified accordingly (hour meters up to thickness of mm (0.31 in) can be installed)Tighten the mounting nuts evenly on both sides