The body I believe look in the how-to there is a ground wire write up in there.

 

yes, the battery is ground close-by to the body. there should be another wire that also grounds moreso near the fender.

 

The thick wire goes to the top of the trans, where the trans and engine meet (engine ground).

The smaller 2 wires are body grounds. Both them are around the drivers fender area.

 

What size is the wire that goes to the trans?

 

I looked in my Ford Publication wiring manual for 2000 Focus:
While it did not list the ground lead, it did list the cable going to the starter
and it is 16mm2
Which is close to 5 gauge
If you are going to buy generic or make it yourself go with 4 gauge rather than 6 gauge because 5 gauge is not available here in the USA
In the American system smaller numbers are bigger wires
E.g. 14 gauge is good for 15 Amps. 12 gauge is good for 20 Amps

 

The engine. The smaller ones connect to the body, and there are some supplemental body to engine grounds at the top of the engine.

 

4 gauge is what i was thinking, so sounds good. Thanks.