Electrical Nightmare

[Miami240z]

I have a thick ground wire on my lower sr harness that Im not sure where to place. It extends furthest to the front of the car and is close to the passenger side relay/fuse box. When its disconnected the car is dead and when i bolt it to the intake manifold the car behaves as described below. Been searching for anything sounding close to my problem for days with no luck.

SR redtop starts up great in my 93 coupe. Few bolt on mods nothing too serious. Car idles and revs fine under no load. go to test drive and notice my lights dim and temp gauge needle jumps when i press the brake. Put the parking brake down and the temp needle shoots above and beyond Hot. Im certain the car isnt over heating so i proceed. Start to reverse and hear a buzzing+ticking sound that increases in speed the faster i go. Sounds are coming from my passive belt computer, ecu, and somewhere beneath the steering column. Sound is present going forward as well. Car also feels like exhaust is all blocked up by 2.5k-3k rpm.

Any ideas? Feedback greatly appreciated.