ok, before i had my fan switch replaces my voltage would stay right around 13 -15 volts. i have a new battery and an alternator thats re-wound to 150 amps. Now that the fan switch is fixed, the fan is on quite a bit of the time, like its suppsoed to be, however now that its fixed when i stop at a light, my voltage drops to like 10 ish..(the yellow line befor the red), if its at night all my gauges dim and the lights dim..is this normal?

 

Thats definitly not normal.
You said you had the altenator rebuilt, so I woudl say at least check the battery.
If the battery is starting to go bad, It could be drawing to much power, or there is a big power draw from somewhere else.

 

rewinding your alternator will produce *less* current at idle, and more at higher rpm's... since it happens when you are at stop lights and such, you're most likely idleing... and your alternator isn't spinning fast enough to keep up with the current demands of your electrical system... if you rev it up to 1500 or so while stopped, do you still have the problem?

 

no, once im sitting if i either put it in neutral (increase rpm's) or rev it its fine..everything goes up..so basically am i hurting anything by doing that?

 

nope, thats pretty much what you're stuck doing with a high output alternator..