Join Date: Mar 2002
Location: Austin, TX, USA
Re: Engine\Frame\Body grounds
X2 to what DJD said.
The block needs the monster ground to carry starter current. The right inner fender ground supplies current to all the body electrical systems - lighting, radio, horn, wipers etc. The engine block ground, besides being able to carry huge currents, also has lots of ignition and alternator noise on it. The body ground will be less noisy. The battery acks like a huge capacitor keeping the block and body grounds from innermingling with each other.
Ground straps aren't meant to carry current. They are for noise suppression. With grounds separated that way (block and body) the two grounds can vary from one another. Imagine how the engine block ground has ignition noise on it. The bonding straps help equalize the ground voltage levels to keep ignition and alternator noise from fuzzing up your AM radio.
The ground strap from the block to the firewall serves another purpose. It gives your guages a more direct return path back to between the instrument panel and the block. Consider if your temp sender's ground return path was through the block, back to the battery, through the pigtail on the fender, through the body...you get the idea. The strap provides a more accurate reading with a shorter path.
68 Coupe, 350 w/ Edelbrock Performer RPM heads, cam, intake, 700R4, Dave's small body HEI