I have a stock alternator, proly the origional, on an 88' 4rnr. I have a measuring device, much like a multimeter, that measures digitally, by plugging it into your cig lighter. So I do not know if the voltage is being read straight from the alt., and nice and clean, or if the V- goes to the batt first , through various cables, etc., then onto my cig lighter.
Anyway, the readings I am getting are between 13.55 and 13.85 volts, depending on what I have on electrically, and the rpms I am turning.
Does this range sound okay, or am I running light on the output?

 

Should be 14 or a bit higher I believe

 

13.5 - 14 at the cig lighter is good. There are several fuses etc along the way.

Better check would be to use a regular multimeter at the battery posts - that's a direct feed from tha alternator.

 

Turn on the headlights, the heater, the radio, the wipers all at once, and then measure.
As long as it is over 13 volts you are fine.

 

14.0-14.4v engine running at about 1200rpm (the alternators max charge rate), measured at the battery is optimal (no loads). Vbatt engine off/key off should be above 11.8v. I replace my batteries if they consistently read below 12v but I run deep cycle, They normally read about 12.6v. I've measured mine at the lighter socket before but wire resistances (lighter socket is only like 16ga.) and fuse resistance fall into play here and can give a false reading. Anything above 13.5v at the socket [should] be ok. But always better to test at the battery.