mind of its own

Depending on what type of 'trip' is created in Basecamp, your GPS will perform in different ways e.g. :-

1) Creating a 'Track' in Basecamp will result in a series of waypoints, (or single point locations), the GPS will plot a straight line from one waypoint to the next one

2) Creating a 'Route' in Basecamp will result in series of waypoints in a similar way to a 'Track', the difference being that the GPS will follow a road, or path to get from one waypoint to the next

'Tracks' are usually used for walking / hiking where there is no roads / paths to follow and should not be used in this case. A 'Route' created by Basecamp can be interpreted by a GPS in one of two ways depending whether the GPS can perform 'Multi-Point Routing' or MPR, basic GPS / Satnavs can't perform MPR so they only use the start and end waypoints of the Route and then calculate a new route using Fastest or Shortest.

GPSs / Satnavs that can perform MPR will follow the exact route as plotted in Basecamp, provided that the map used in Basecamp and the map used on the unit are the same, if the maps are different you may find that certain roads used in Basecamp are not present on the unit and an alternative route will result because the unit will only use roads if they are present

The Garmin link (Click HERE), suggests that the Zumo 390 can accept downloaded routes created in Basecamp, however it doesn't specifically state that it performs Multi-Point Routing, have a look at the instruction in the link above, Units that have 'Trip Planner' in their menus usually will perform MPR

Page 6 of your user manual may have the answer to your problem, try using 'Curvey roads' :-