Reckon you have the famous 'spider'.
You can bypass the spider altogether using a small harness available from Land Rover .
Of course there could be other reasons for the occasional loss of power e.g. my brothers 97 300 Tdi was doing something similar which got progressively worse (including a few scares at junctions etc ) until it refused to start at all. Turned out to be a small black wire attached with the main earth behind the battery was loose . Tightened it up and fine since .