Quote Originally Posted by SplitBusVanatic
A long shot but worth tryin.
Check your earth strap coming off the battery.
These can get loose sometimes if battery mounting points were removed and left off.
Or a smaller battery put in.

Other than that.

Might be the abs hall sensor on right or left rear wheels.
Can't remember which side.
Used to happen to me on a '98 E39 I had.
I would cycle on an off the key,(while moving). Problem solved for a while.
Never did fix it. Car got sold on eventually. Owner was aware of the gremlin.
Be no harm to plug it in James.
have been messing with the battery when wireing the seats,will check it over tomorrow.mightnt be tightened or something,fingers crossed..