Voltage problem?

[Skax]

your car may have a pcm that keeps the voltage set where the car "thinks" it'll be happy.

I know some cars are weird and you can turn on headlights to increase voltage

Yea I didn't even think about that I'll try that if not

Oh we'll lol

[reedal]

13.3 at idle isn't really a voltage problem, but if you want to have a higher voltage, then i would suggest a voltage regulator for your alternator.

[deadbroke]

Well that's a bummer because some amp manufacturers test at 14 volts

[reedal]

They do test at that. Most birth sheets/specs for amp ratings are shown at 14.4 volts. But in reality, you're not always going to have 14.4. As OP posted, at ALT he's reading 13.9 which isn't bad to me even if not ideal, but at his battery he's reading 13.3. There's voltage drop to account for due to resistance through his wiring and (possibly) loose and corroded terminals. Not knowing what vehicle or how old the alt is, it might just be a worn out alt if it has some age on it. My explorer battery reads 13.2 at idle, 13.8 @ 1700-2200 rpms on a cheap digital volt meter, with a recently replaced 130A alt, no big three, and a kicker cx1200.1. So to me, OP's 13.3v at idle doesn't seemt an issue, but some with more experience and knowledge than I might say I'm an idiot and wrong.

[Skax]

Yea alt is a little old it's A 2003 mustang

[reedal]

I would say to either:

1) accept your current voltage and charging

2) find a new alt at napa or some other store/website

3) purchase a new alt that has a higher output in case you plan to expand your system which requires more current draw. Find one that outputs enough current for your system and stock electric