From http://www.w8ji.com/mobile_ground.htm: Over time, vehicles with positive grounds disappeared. As this happened, manufacturers stopped using the more-expensive and more-complicated floating negative power bus system. Many vehicle manufacturers, and most aftermarket equipment manufacturers, never re-thought the systems others were using. Manufacturers carried over the acceptable negative fuse idea appearing in ground independent power buss systems, which could also use a negative battery post connection. Manufacturers misapplied the allowable fused negative battery post connection to equipment with internally grounded negative bus systems. Not realizing the safety hazard, they continued to fuse both negative and positive radio power leads and often advised direct battery post negative connections. The battery post connection actually created ground loop, fire, and equipment safety hazards. This terrible idea has permeated the aftermarket accessory market, including amateur radio, audio, and performance or race car electronics markets. For example, MSD Ignition's installation instructions advise a direct battery post negative connection, putting the vehicle's distributor, the MSD box, and other electronics at risk. Although absolutely incorrect, a popular assumption is fusing the negative lead can protect internal and external equipment wiring, including gauge, computer, speaker, microphone, key leads, and antenna connections from open battery ground connection damage. My mobile installations have always had the negative lead from the rig connected directly to chassis, near the rig. It's not possible for a blown fuse to allow a high current return path via other path(s). The ONLY fuse(s) are in the positive lead, with a fuse AT the source.