There are three main locations to look and find an issue on the connections. Those are the main harness, connection to the pigtails, and the terminal block.
1. Check the terminal block on the rear transom for loose screws and wiring ends on the conenctors. This is the first culprit.
2. Check the connection between the unit harness and the boat harness, which are brown Amp plugs, These should be tie strapped together to prevetn loose wiring.
3. Check the main harness connection at the unit itself, behind the fastening strap to the unit.
DO NOT place the plugs in the wrong location. BE ABSOLUTELY Sure that you have them on the proper pins locations.
Also check your compass, speedo, barometer and temp readings. If one of these in inaccurate, disconnect the sensor or recalibrate them.
Good Luck!
BCB