im getting a suddenly drop in voltage as if im grounding out somewhere,it only happens when im stopped and idling.Where is the most obvious place to ground out.

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1987 Trans AM GTA
305 5SPD
Hypertech airfoil
gutted maf
kn filter
High Flow Cat,
3"Walker pipe
Dynomax Super turbo Muffler
TB Coolant bypass
Lubricated by Mobil 1 Tri-Synthetic

 

just about anywhere a hot wire runs close to metal. you can buy a tool for locating shorts.

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ICON Motorsports
1st & 3rd
MM Black Diamond 538 F&AM

 

Without knowing just how much the voltage is dropping, it may or may not be a problem, as the alternator will always produce less current (thus less voltage) when moving slower (engine at idle).

Depending upon how low the voltage drops will depend upon many many things (battery state of charge, battery condition [if the battery is bad, it could cause excessive load to the alternator...], accessories being used, alternator pulley slipping, etc.).

With all the accessories off, it should be able to maintain at least 13.0 volts at idle, probably more.

With all the accessories "on", including both fans, blower fan, lights, etc., it will be normal for the alternator output to be unable to keep up with the load at idle. If this occurs, the battery will then provide the balance of the current needed. When the battery is supplying current, voltage will then be ~12.5 volts, and begin to drop even further. The speed of this reduction will depend upon the amount of current being provided in addition to the capacity/condition of the battery.