Odd Alternator issue...input would be appreciated.

[Stevorama]

Hi all,
So a little background on my issue...my alternator went bad so I upgraded it to the 240A one from turbobuick.com. I have also already removed the fan control relay since it was causing a drain on the system. New (3 month old) battery, removed the voltbooster that was installed by a previous owner. Yesterday I decided to start the stereo work on my car so I began with running 0 gauge wire to the trunk and upgrading the battery wire and ground under the hood to 0 gauge as well. I started the car after upgrading the alternator wire and ground just to make sure everything was kosher. Yesterday, the battery was at around 12V with the car off and it was at 14.5V at idle. Revving the motor the voltage would increase to around 14.6-14.7 volts and that was about all. Seemed pretty standard to me. This morning was a different story. The battery was reading 14.7V with the car off and when I started it it shot up to 18V. And that's where the problem is at right now. I don't understand how upgrading the battery wire could have caused this, but that's the only thing that I've done before this conundrum that I'm now in. Anybody have any input as to what I could have done wrong? Both the battery and alternator are 3 months old, and were working fine before I upgraded the wires. Everything is ohming out correctly and my bulb in the dash for alternator exciting is working correctly. So...any thoughts out there?
Thanks,
Steve

 

[TurboBuRick]

First thing I would do, remove the cables and test battery it by itself.

 

[tom j]

What is the voltage on the battery while cranking?

 

[pacecarta]

when you removed the volt booster what did you use to connect the alternator to the brown wire on the harness
the brown wire needs to go to the L port on the connector

there is also an S port for sensing the voltage , if its connected an its not at 14.2v say its 12v or less (like through the lamp circuit brown wire) the alternators internal regulator will compensate until it sees 14.2v at that port, that would explain the voltage at 3-4v over norm

 

[Stevorama]

The brown wire is going to the L wire off of the pigtail. As far as the voltage sense wire goes...what color is it supposed to be? Only thing I hate about this car is that most of the stuff the other owner added seems to be hacked electrically. I think the battery just might be bad...taking it to get it tested now as it seems that even though it meters at 13.5 V it doesn't have enough juice to crank the motor over anymore. I'll post an update in a bit. Thanks for all the advice so far.

Thanks,
Steve

 

[mikestertwo]

What are you using to measure the voltage and where are you measuring it? The reason I ask is you said the battery voltage was reading 14.7 volts "with the car off" and then 18 volts after you started it. The battery should not be reading 14.7 volts without the engine running. That's about 2-2.5 volts too high.

 

[Stevorama]

I'm using a MAC Tools DMM. I know it's reading strangely, but I can assure you I'm metering it correctly. I did car audio/video/security for 8 years so I know my way around a meter. Battery tested fine...good thing this car isn't my daily driver. I'll update once I figure out what the problem is. Any more input will still be appreciated.
Thanks,
Steve

 

[mikestertwo]

What does a scan tool say the voltage is?