First go through all the fuses ,turn them in their holders .If you still have the white metel type, then you need to change them for copper or brass . Now check all earth points,remove them one at a time.Clean the conntact area and put a dab of grease on before you refit them.Then look at all your small vacuum pipes for split in any rubber joining ellbows. Another item to look at is your OVP relay ,it sits at the back of the battery .You will have to pull the plastic membrain off to see at the back .The OVP as a fuse on the top,check the fuse or fuses some have two.Then you can come back, let us know how you get on.