Partner Earth problem?

[qert6]

Hi, My partner has a couple of problems that I think might be to do with earths but i'm not sure where to find the points that I need to check. The first problem is the wipers are really slow and sometimes stick. This is intermittend and seems to be worse in the damp conditions. The wiper motor on the van looks to have been changed and all the linkages are covered in grease as though the previous owner has had a go at fixing this. So I'm assuming that the mechanical side of things and motor are ok.
The second is the heater blower, it sometimes works, sometimes is really weak and sometimes not at all. This is the same on all settings. The blower and wipers do not seem to sync so that they both work and dont work - 2 bad earths? or something else completely?

Any pointer to where the earth points are that I need to be looking at would be appriciated or any other ideas that could be casuing this.

I have checked the voltage when running and its 14.4V and other heavy electric users like the headlights are working fine.

[qert6]

Oh Its a 2001 1.9D