There is a controller on the bars and one under the set, connected to the battery.
With the bar controller and the grips unplugged, the seat unit blows the fuse. Put a 30amp in, it blows.
Before you say it, no there was no pinches in the power cables. They are only 200mm long, under the seat.
There is a lot of reviews on the web. Lots of people have had no issues at all. Others have had no end of problems.
I've replaced the whole thing twice. First one lasted 3 weeks, the second 10 minutes.
Now looking at my options of different units.
