That extra ground can be attached to any convenient body panel screw, or just scrape a spot down to bare metal and drill a hole for a big sheet metal screw. Electrons aren't picky about where they go on the way back to the battery, and since electric current approaches the speed of light, a few inches plus or minus on a car body makes no difference.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!