This happened to me just a few nights ago. Have a look at this thread:
https://z4-forum.com/forum/viewtopic.php?f=45&t=91766
I'm just about to order some of these heat shrink butt connectors, some extra wire, and some heat shrink and give it a go this weekend.
https://www.halfords.com/workshop-tools/garage-equipment/fuses-electricals-fixings/halfords-heat-shrink-butt-connectors-hef110-15-amp