You have to remember that our cars are built of layers of sheet metal. Between each layer there is a layer of non-conducting material.Between the strut towers there are some where between 12 and 18 layers of this sound deadening/water-proofing material. In order for the ground connection between the strut towers it relys on just the spot welds to conduct. Since you cannot really rely on those connection for a good ground, why not improve your chances and ground each body panel directly?
With the engine, the ground work in the same way, between each metal component of our engines there is a gasket of non-conducting material. We rely on just the bolts for ground, where any oxidation,grease,or assembly lube can cause a ground fault.
This is why I added grounds to each , and scraped the paint and then cleaned with a degreaser each and every ground connection, such as,tower,firewall,transmission,head,block,alternator,body,original ground locations ( these can be found by looking for groups of white w/black stripe wires in a flat lug). Even these grounds are not cleaned, there is primer and paint between each metal part, making for a poor ground.
I worked for 13 years in an auto assembly plant and saw how they build em, and yes it was a Toyota Plant for those that ask.
