baffled with charging issue

[N4aRush]

first off...sorry if this is in the wrong place
i have a problem that baffles me beyond belief.
i have an 89gt (original motor) i have udp's and a 3g alt.my volts at idle fluctuate and vary from 14.5- 13.7 with nothing on.with lights on 13...with heater 12.2 or so.sometimes its lower..so low that i cant even play my radio at idle.
also some days when i start it up...my volts are steady at 14.5 and my guage reads a hair above half way.i can turn on my lights and the guage will drop to a hair or more under halfway.when i turn the lights back off...sometimes the gauge doesnt move back to above midway...almost like it doesnt recover
another strange thing to me is that some days my volts will flucuate like i have a lopey idle...but my idle isnt flucuating at the time the volts are.
i have double checked all my 3g alt wiring.not using the original fusible black and orange wires.have 4g power and ground wires.

ive been told my udp are to blame and a over drive pulley on the alt would fix this.
reasons for this belief is- for one when i have no volts i can barely put my foot on the gas...not even enough to see the rpms move...my volts go back up...the second is because i dont have this issue driving.while driving i can run everything and the guage stays a hair under halfway...

sorry for being so long...hope i didnt leave anything out.any insight would be appreciated as this is my first mustang.

*forgot to add that the ground from the back of the motor to the firewall is attached and from battery to block is new.

 

[txstang84]

Welcome to StangNet!

If you're talking about that puny little ground strap between the bellhousing and the firewall, you might wanna get something a little more substantial to bond between the block and chassis...or is it 4G as well?

It sounds, intially, like your voltage regulator is being a punk, or you have poor grounds, or possibly inconsistent volts to your field wire, perhaps.

 

[Incon]

What shape is the battery in?

 

[f8tlfiveo]

If you are looking at the stock gauge I wouldn't be worried.. Get a good gauge. The stock gauges are junk. My stock gauge acts the same way but everything is fine.

 

[Noobz347]

Relocated to Technical Forum


As for the problem... Remove the UD pulleys and report back. If you're bringing the throttle up just a hair and everything reads normal then alternator is not spinning fast enough to exciter to come alive.

 

[txstang84]

...you're an exciter

 

[Blown88GT]

...ive been told my udp are to blame and a over drive pulley on the alt would fix this...

Yes they are & yes it will.
From here
...If you do not get enough ouput voltage at idle, replace the standard 60mm pulley with a 1 3/4" (44mm) overdrive pulley from Auto Specialties (ASP520004). It's easy to monitor voltage on the go, make a cable that connects your DVM to the cigarette lighter and watch it under all conditions. The voltage will drop off when the engine/alternator get warm; this is normal. When the load increases, i.e. electric fan comes on or you turn the AC/heater blower on, the voltage will normally drop. It would be nice to keep the voltage at idle above 12.6V, which is the voltage of a charged battery, otherwise you will be drawing currrent from the battery (discharging it) instead of from the alternator..."