Hello,
I recently purchased a 73 Mustang.  I've enjoyed the forum here and have found some interesting things.. I have a question though regarding the Alternator gauge.  

What is the normal behavior for the gauge?  Mine is generally in the middle at speed, but when idling it sometimes bounces between the middle and the charge side (to the first line on the gauge).  If I turn the turn signal on, it also bounces a little bit in sync.

I am just wondering if this is normal, or if I might be seeing early signs of a bad alternator or something.

thank you!  

That sounds about par for the course for a 1973 Mustang.  You could help that situation a bit by putting in a 100 amp alternator, but as long as that alternator keeps your battery at peak, then you are good to go.  Welcome to the world of the classics.  You aren't running some woopty-doo high powered stereo unit are you?  

Hey There.. Thanks for the reply.  No, no massive power system - just the stock original AM/FM radio

I appreciate the info.  Just trying to learn about the car and having fun with it.  I'll post a pic.
thanks,  

My ammeter tells me so nearly nothing.  If I am driving at night, I leave the lights on when I shut the engine off to see if they dim, theory being that it was probably charging okay if they do.  I also made a voltmeter that plugs into the cigar lighter and I use it occasionally to make sure all is okay.  

I have owned ( 3 ) 69 Mach I who's altenator gages hardly ever move. Just moves slightly to the left under load. This is typical for many of the Mustang cars. The suggestion for using a cigarette lighter volt meter is a good one. I have a friend who lets me borrow his to check my car from time to time, it works really well.  

I own a 71 429 & took the whole centre dash out to get the gauge tested. Dos'nt answer your question but they do'nt do much, except when the battery is down, but it quickly comes up to the centre.Could be a loose contact???  

Thanks for all the info.
I bought one of the cigar lighter volt meters for $12.  I'm not very experienced with electrical though  Can you please tell me what to expect from the cigar lighter --- 12V all the time? Should it dip down?  When do I need to worry about battery or alternator?

Thanks again  

12-12.5 volts when the car is not running.  Drop to maybe 10 during cranking.  13.5-14 volts while running.

High voltage (15+) will overcharge and dry out your battery and burn out lights early.