Its starting to sound like a good earth is the key to a few things
hehe - yes. In many cases "The French Connection" is the problem.

be it earth, or connections in general.
I have found that the most of the connectors on the car outside the cabin, are heavily corroded, and if you can get them apart at all, they most often crumble.
Every single one of them needs attention, - but then again, there aren't that many.
The edge connectors on the fuse-board is of the same type, and as the fuse-board is only single-sided, those are a common problem as well.
On the front of the "torpedo" - the wall separating the cabin from the front , there is a connector for the wiper motor and (I think) the interior fan. This one is often pretty corroded.
Then there are a few earth-points, - one on the chassis running straight from the battery, another near your left knee while driving (behind the carpet) and then one from the engine-block - forgot where (as my car has a non-original engine). I think it runs from the gearbox to the chassis in the left hand side.
/Lennart