Alternator charge

12volt systems you want the out put of the alternator to be 13.5 volts. Anything less you are draining your battery. Simple things to check before you pull the alternator. There is a fuse, it will be a big one, probably 60 amps. Make sure the connections on the back are clean (no oil or any corrosion). I lite sanding with some 120 grit will clean the connections. Remember! Bright shiny surfaces conduct best. Check your alternator mount for corrosion. Check your ground wire from the battery to the frame. There should also be a wire that goes to the block! Check your positive cables.

If all of these fail to give you 13.5 volts, then yes you need to get your alternator off to the shop. Hopefully just brushes, but be sure to have them replace bearings too.

 

On the Columbia I drive if it does not maintain 14.0 volts running down the road with the light on, I check my batteries. Not only with a volt meter but also a hydrometer. I have the best luck with it changing batteries together. If my voltage drops below 13.9 I know I have a problem, so far its been a battery on the way out.

Im a little touchier than most on battery and charging system condition as we do alot of work in really remote areas of Nevada and Ca.

So when in doubt change it out. Make sure all connections are clean, very clean wire brush, sand paper clean and sealed after clean assembly.

 

If you have charging, problems you want to disconnect the batteries and charge them independently with a regulate charger, leave them sit for about 4 hours after charging and check the voltage it should be above 12.6 volts while this is happening clean all the connections on the starter, alternator, batteries, and grounds. Do not forget the cab grounds. Clean the connections and use die-electric grease.
If you have any week batteries change them all.
If you have a good multimeter it will have a min max function press the button with the meter on voltage, then start it, it must above 9.6 volts and should be above 11 volts.
When the truck is running down the road the voltage at the batteries must be above 13.8 volts to properly charge the batteries. 14.2 is OK anything above that will overcharge the batteries. 14 volts is perfect.

 

As always, excellent post JohnP3....

 

alternator on front of motor prolly has a belt goin to it starter at back of motor prolly on the drivers side

 

Since dec, 2006 my truck sat... first for 17 months (quit driving) the again for 11 months (accident)... I was surprised that all the batteries were still good... didn't expect that.

I usually change my batteries every two years... but the Mack batteries I have in my Pete right now are 7 years old... and still going strong. Amazing. I fried an alternator right in front of a Mack dealer... I usually don't shop for Pete parts at a Mack store!

Now if those Macks were just a little more friendly to work on...