3g Alt Swap and lights are surging still

trinity1988

New Member
Jan 16, 2011
17
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Redmond, OR
I have an 88' mustang that was recently purchased. It is a 347 with H/C/I and the usual goodies. I thought the car needed a 3g swap but after investigating, I realized it already has the 3g in it. The original owner mentioned it needed a tune, could this help the surging lights situation?
 
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Tune wont make a difference.

Does the car have underdrive pulleys on it? If so, either swap the stock pullies back on, or at least put an overdrive alt pulley on the car.

Even with a 3G alt, the alternator needs to spin at a minimum RPM to produce full charge. Based on the limited info you've provided, i'm assuming your surge happens at idle and goes away with a small bit of throttle? If so, need to spin your alt a little faster
 
I will agree, either the car has underdrive pulleys or you could have a 3G that is not putting out the correct voltage. I am not much of a fan for UD pulleys myself
 
Hows the battery? I would at least get the battery load tested to make sure its good. Also get the alternator tested, It definitely could be cause by UD pulleys but check the basic things first. Also check the wiring and make sure he upgraded to a larger wire size and didnt use the factory wiring.
 
Yup, it has the UD pulley on it. And yes, the surging lights only happen at idle. Any ideas on where to get a stock one, or even which size to get?

Good point on the battery test as well as the alt. wire size. I will check that out for sure. Thanks for the HELP!!
 
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I run the 1 7/8 pulley on mine. Had to use a 5/8" washer as a spacer behind it as the pulley will contact the case without it.

I use this, with underdrive crank pulley and underdrive water pump pulley. No issues at idle with heat and lights on

EDIT: sumittracing also sells these if you search for the p/n. might be cheaper shipping