This diagram shows the grounding strap from the battery where it grounds to the body under the rear seat. (#1 in the diagram). The threads on the bolt and on the body get rusty. It is also bolted to a painted surface. Having a similar problem on a 00 SSEi, after cleaning up the bolt and the threads in the body, adding a star type lock-washer under the lug to bite better through the paint, and adding dielectric grease - the problem went away. It has helped some, but not others. Either way, it'* a good preventative maintenance step.
Black 2000 SSEi, Silverstar Headlights, Angel Eyes fogs, 3rd brake light overlay, hi-flo cat, drilled 180 degree thermostat, Intense FWI, PCM, shift kit, and 3.4 Pulley. Solid front mount.