85 300zx mechanical issue with video
 

So my 300zx turbo when it starts runs rough. The lights will pulsate and a shop told me the car isn't grounded. In this video at about 1:46 as I let the car run, there is a hole in the firewall by the battery where they said a wire needs to go from there to the negative cable. Also, after it runs a bit, the car will start to slow down. The idle decreases like its running out of juice but if you rev it up it goes back up and continues to run for a few seconds. This is after its run for about a minute. That is also in my video.

http://www.youtube.com/watch?v=O-AHlzTp1kg

I would use a voltmeter and watch your battery voltage drop while its running. Yes, this can be caused by bad battery cables, battery itself, and even a loose alternator belt. The belt on my 87t was so bad and crusty it would not grip at all and charge. Electricity takes the path of least resistance so, if anything isnt allowing it to flow freely it will cause issues.

yes the ground cable should go first to the body then to the starter. my 85T had the same hole. pic is from my 86T showing the proper ground. On my 85 i ran two 10 gauage wires from the negative terminal to each side of the engine room to a convenient m6 bolt that went into the body (there are plenty of choices). worked on that car. i would probably now weld an M8 nut to the fire wall and ground it there then to the starter.

GEt your battery load tested. Be sure you have clean, tight corrosion free terminals on both ends of your battery cables. Be sure the ground (negative) cable goes to a bolt into the frame before going to the starter. grounding through the starter is not a reliable connection. Z's don't like low voltage. causes the electronics to act funny. it is possible to have enough amps to crank but not enough voltage to run the electronics. If you have one size fit all cheapo clamp on terminals they are a problem waiting to happen.

Clean the connectors for the maf, ecu and tps. Deoxit by CAIG is probably the best connector cleaner on the market. spray with CorrosionX after cleaning and before putting together this will help prevent any further corrosion.

once again I seem to be unable to post a pic to this forum and searching for the answer yeilds nothing. keeps telling me I already posted it once. anyway where the hole is there used to be a threaded hole. the original ground strap had a square copper tab crimped to the cable. this then bolted to the body where you now have a hole thence to the starter.