I upgraded my sparkplugs to bosh platinum 4's and my cables to msd's 8.5mm. Now suddenly after driving the car for a while when I let go of the gas pedal at about 40 mph my voltage gauge drops to the bottom and my lights dim and the car feels like its going to stall. Also when the car is parked and idle it feels like its going to turn off but it does not. Does any one have an idea of what could this be. Also if I do not use the car for more than 24 hrs it will not start after wards or start very weak. I changed the battery but it still doing the same thing. PLEASE HELP!!!!!!!

 

I doubt if plugs and wires will do this, mostly a set of quality wires. Check the voltage at the battery with car not running (like first thing in the morning before you start it) Then start it and check the voltage again. At rest the battery should have atleast 12.2 V and running you should be well above 13 V. If you arent then it sounds like the diodes in the Alt are dead. Have the Alternator rebuilt by a reputable shop. It only takes about a half hour and is cheaper then buying a new one.