Use an inexpensive digital voltmeter. Sears, Walmart, and Radio Shack have them. Don't waste your money on the expensive ones. They don't work any better, they just do a lot more functions that you don't need. If you have a Harbor Freight Tools store nearby, they have one for around $7.99 that goes on sale quite often for $2.99. Just be sure the test leads are plugged in tightly so they make good contact. Set it to the 20 volt DC scale for the best accuracy. That means it can read anything from minus 20 volts, (hooked up backwards), to plus 20 volts. Higher scales will work too but you will lose one place after the decimal point of accuracy. You need to read to the tenth of a volt.
Put either lead, typically the black one, on the battery negative post or a clean, paint-free point on the engine block, and touch the red lead to the point you want to measure, in this case, the green wire on the back of the alternator or in the plug for the regulator.
The voltage regulator is rectangular, about 3" by 4", an inch thick, and has a black triangular plug with room for three wires but it only has two in it. The blue wire is in the middle and the green wire is in one side. There is a metal band that you have to squeeze on the sides to release the plug. That regulator is usually silver but I've seen black and gold ones. Two bolts hold it to the firewall. They are not straight across from each other and are not in a symmetrical pattern.
You might have an orange or red box on the firewall that almost fits that description but it is smaller and has different wires and plug. That has nothing to do with the charging system.
You can use the voltmeter to measure battery voltage too and to make a quick test on the charging system. A fully charged battery will measure very near 12.6 volts. A good but discharged battery will read around 12.0 volts. A defective battery with one shorted cell will have about 11.0 volts. When the engine is running, if the charging system is working properly, you will find between 13.75 and 14.75 volts. It might creep up a little from time to time, especially in cold weather, but anything over 15.0 volts is undesirable. The regulator has temperature compensation built in. That's because recharging the battery after starting the engine is a chemical process and chemical reactions slow down in colder temperatures. By bumping up the charging voltage a little in cold weather, it helps to fully recharge the battery more efficiently.
Tuesday, November 23rd, 2010 AT 4:29 PM